Why didn't Fischer play Karpov

Fischer's mental state.  Some interesting background.

https://psmag.com/a-psychological-autopsy-of-bobby-fischer-f757852a2910#.g9vcubhrh

get a massage

Those who still cling to the idea (advanced by Kasparov) that Fischer came up with those crazy demands in order to avoid defeat at Karpov's hands, should have a closer look at the 1975 WCC cronology:

- Sept 1973 - Fischer "proposed" his changes to FIDE

- Feb 1974 - Karpov wins candidates quarterfinals

- May 1974 - Karpov wins candidates semifinals 

- Jun 1974 - Fischer resigns the title

- Nov 1974 - Karpov wins candidates final and earns the right to challenge Fischer

- Apr 1975 - Karpov becomes WC by default.

...and the rest, as they say, is history. 

The point is, Fischer didn't even know for certain whom he would be facing when he made those demands :)

For "x" or "y" reason, Fischer did not want to or could not play.

Karpov was the legit champion !

Saludos 

Correct, Fischer resigned the title in a telegram dated June 27, 1974. Karpov resulted as World Champion, by winning Final Candidates Match against Korchnoi. But let's compare how they qualified:

On November 22, 1974, Anatoly Karpov (1951- ) won the right to play Bobby Fischer in the 1975 World Chess Championship after defeating Viktor Korchnoi (1931-2016) in the Final Candidates Match, held in Moscow, with 3 wins (games 2, 6, and 17), 2 losses (games 19 and 21), and 19 draws out of 24 games played. The proportion of draws was about 79%. In the 3 candidates’ matches, Karpov played 46 games and lost 3 games. By comparison, Fischer demolished all three of his candidate opponents in only 21 games. He beat Taimanov 6-0, Larsen 6-0, and Petrosian 5-1, with only 3 draws and only 1 loss.

So the final answer is: because he (Fischer) resigned his title earlier (before Karpov qualified as challenger)

Money requests from Fisher. 

Excellent point, but of course Fischer haters will conveniently overlook that fact.

Funny thing is, we're told over and over again that Karpov and Kasparov were a tough new brand of chess professionals. When they won victories by a not so convincing margin, it was usually attributed to the fact that they alledgedly had to face younger, more energetic, and more accurate players than Fischer did.

Yet, with exception of Beliavsky, both Karpov and Kasparov faced players from Fischer's era during their respective candidate matches of 1974 and 1983, who were 3 and 12 years older respectively. And don't think Kasparov's performance was any more convincing:

6-3 against Beliavsky (aged 30)

7-4 against Korchnoi (aged 52)

8.5-4.5 against Smyslov (aged 62, LOL)

Fischer's opponents in 1971 were 36, 42, and 45 years old respectively...

"Excellent point, but of course Fischer haters will conveniently overlook that fact"

Fischer scored a higher percentage in his Candidates matches against other opponents than Karpov did in his Candidates match against Korchnoi. Then it's another thing what you want to conclude from this, or how much you want to call others Fischer haters. One could just as well state that Karpov scored a higher percentage in his match against Spassky than Fischer did in his match against the same opponent, and talk about Karpov haters overlooking this fact...

who am i?

That part is true, but it must be said the percentage difference was 62.5% vs 63.6%. Hardly something to write home about.

Aside from being 2 years older (which might or might not matter at the highest level, especially when the player in question has already peaked), Spassky was never the same after Reykjavik. The punishment for allowing the crown to fall into the hands of the enemy was real, not just a figure of speech. Being marginalized and deprived of support made a crucial difference in an era when computers were not available. I guess that doesn't matter either.

"I guess that doesn't matter either"

I just find it a tad selective to see their scores against the same opponent as less to write home about than a comparison between Fischer's result against 45+ Taimanov and Karpov's against Korchnoi, and that the latter would be something Fischer haters conveniently overlook since that would be so much more telling :-) I don't think results even against common opponents say much, and I don't think Carlsen's winning the Candidates in 2013 with a smaller margin than Anand won in 2014 say much about Anand being the better player of the two either. 

I guess in the absence of an absolute and objective comparison criteria, people always fill in the void with speculation. In the Fischer vs Karpov debate there's one extra variable: Fischer's strength after 1972. Nearly all top players have had longer careers, so pinpointing their peak year(s) isn't such a difficult task. We know when Karpov and Kasparov peaked (at least rating wise), we have seen them past their prime. In Fischer's case, all data we have is up to 1972, then a blip on the scale 20 years later, then nothing. So we will be forever wondering whether he would have started to fade in 1975, 1980, or 1972.

In the light of all this, plus the 1975 WCC cycle cronology I mentioned earlier, people of Kasparov's caliber shouldn't engage in this sort of smearing campain. 40 years is certainly a long time and many people have forgotten the details surrounding Fischer's forfeit, but Kasparov should have been aware of them. 

Maybe Fischer is the most talked about world chess champion, but he also seem to be the most reviled. And when it comes to Kasparov and his speculations on the matter, ignoring facts and cherry picking match performances, one could easily dismiss the whole argument as nothing more than an attempt to boost the profile of the man he himself defeated nearly 10 years later (even though just barely). In that way Kasparov could - and did - indirectly claim he would defeat Fischer in his prime without being labelled a douchebag. 

#98 alinfe - Five points and a gold star!
"As I made clear in my telegram to the FIDE delegates, the match conditions I proposed were non-negotiable. Mr. Cramer informs me that the rules of the winner being the first player to win ten games, draws not counting, unlimited number of games and if nine wins to nine match is drawn with champion regaining title and prize fund split equally were rejected by the FIDE delegates. By so doing FIDE has decided against my participation in the 1975 World Chess Championship. Therefore, I resign my FIDE World Chess Championship title. Sincerely, Bobby Fischer".  27 June 1974

Moscow 16 Sep 1974 to 22 Nov 1974 Karpov v Korchnoi.
So yeah the Fischer paradox was *not* fear of losing to Karpov

With hindsight I am in the camp of the challenger should conclusively dump the champion.
See Botvinnik who had to win a serious tournament to replace the late champion Alekhine.
After which the "rules" were pretty much set by him such that challengers had to win tournament followed by match play while the champion was allowed a straight re-match.
What Fischer wanted was a return to the nineteenth century Steintz position of a conclusive match play win by the challenger.

"people of Kasparov's caliber shouldn't engage in this sort of smearing campain"

I fail to see Kasparov's opinions on Fischer as some sort of smearing campaign, on the whole they are quite objective. Fischer's opinion on Karpov and Kasparov were that they were dogs, cheaters, criminals etc though and that sounds a bit worse than Kasparov's opinions on Fischer...

"What Fischer wanted was a return to the nineteenth century Steintz position of a conclusive match play win by the challenger"

What Fischer wanted no one knows with any certainty, but it is difficult to see his demands as meaningful. To still be the World Champion if Karpov beat him 10-9 would maybe have been practical, but no one would have found that a satisfying outcome of a match that could take a year thanks to Fischer's other demands, that FIDE amazingly agreed to :-)

Fischer wasn't mentally sound...

There was no scenario of Karpov beating Fischer 10:9. The match would be drawn with Fischer keeping the title in the event of a 9:9 tie. 

The reason Fischer did not play Karpov is that he [Fischer] felt he had too much to lose and not enough to gain if he played Karpov.