Too much work to become a GM, he like teaching and writing stuff.
Jeremy Silman

I believe he retired from serious tournament play. As kco mentioned, he does more coaching and writing now.

In many things, being good at something does not necessarily make one a good teacher. In my profession, music, many natural talents, or 'geniuses', never had to teach themselves anything, or if they did they were so young it would be hard to translate the experience to an adult. They can simply do it. Therefore, it would be impossible for them to understand how one learns something for the first time as an adult or teenager.
Also, the GM field is very thin in America, and it is much more difficult to attain GM norms, and in Silman's active years it was even more so. I believe that if Silman was born and playing actively in Europe, he would have been far more likely to attain a GM title due only to the difference in environmental conditions.

That might be true in Russia, and a few other countries in the former east block SchachMatt, but there's hardly an incredible amount of GM's in Sweden, Iceland, Germany and so forth.
Truth to be told, the whole "America is the hardest place in the world to get GM norms!1!111!one!!1" whine that some American titled Non-Gm's do is getting old quickly.

While I agree that Jeremy Silman is a great teacher, since when is greatness measured by being a consultant in a Harry Potter Movie?

To give an idea of how difficult it is in the US , compared to Europe, to play FIDE rated chess and get any kind of norms consider this : I played chess for 25 years in the USA ( all in the Southeast ) and I dont believe I had a single game that was fide rated. Also....... in those 25 years I played a grand total of 5 or 6 GMs ! I moved to Europe and suddenly all my games are fide rated and I have played as many as 4 GMs in one 9 round event ! In many events I have played 2 or 3 GMs and in one 9 round rapid event I played 6 titled players in a row..... 4 IMs, 1 G and 1 FM ! I was in a state of shock to adjust to the much stronger opposition I faced here in every tournament ! The majority of tournaments I played in , in the USA, didnt even have a single GM or IM playing. In just 2 tournaments in Europe I faced more GMs than 25 years in the USA.......

Travel costs play a significant role. We have numerous tourneys every weekend in North America, but the closest with good master presence may be 4000 km away. In continental Europe you apply your bicycle's brakes a little late and you've crossed two borders and passed six IM events. We'd called you spoiled, but we remember how quickly an invading army can move there and we respectfully keep our mouths shut.
I believe I’ve found an error in the Opposition problem in Silmans video “How to Plav Chess” (Lesson 18). The problem is “Black to Move and Reach f1, g1, or h1 by Force”.
Starting with move 8. Kh1 Kf6, if the white King moves to the black square h1 (instead of g2 as shown in the video), the white king is in distant opposition with the black king on a black corner square in a four corner box with all the corners black. The black King can be easily blocked from f1, g1, or h1.

I believe I’ve found an error in the Opposition problem in Silmans video “How to Plav Chess” (Lesson 18). The problem is “Black to Move and Reach f1, g1, or h1 by Force”.
Starting with move 8. Kh1 Kf6, if the white King moves to the black square h1 (instead of g2 as shown in the video), the white king is in distant opposition with the black king on a black corner square in a four corner box with all the corners black. The black King can be easily blocked from f1, g1, or h1.
Hmm. I believe you are talking about the series of videos sold by "The Great Courses."
Those aren't available here and I have no way to verify what you are saying.
Perhaps you can post a diagram showing the position.

if the white King moves to the black square h1
Not sure what you’re talking about, but h1 is white, so it’s a little confusing. Maybe post the position so we can have a look?

There are players of GM strength who for one reason or another don't try to complete the technical requirements for the title. The difficulties for a US player are well expressed by @TheOldReb in #8, above.
Another example is my old friend, Milan Vukcevich. He was the Yugoslav junior champion and drew a match with Bent Larsen before emigrating to the US. He got his Ph.D. and became a university professor and later the Chief Science Officer for General Electric Corporation, as well as a nominee for a Nobel Prize in Chemistry. Despite OTB chess becoming more of a hobby, he became rated #75 in the world, tied for 1st in the 1969 US Open, and came in 3rd in the 1975 US Championship. He also became a Grandmaster of Chess Composition. Despite all of that and defeating a number of GMs in OTB play, he simply was not able to play in tournaments in which a GM norm was possible, because he focused on his real career.
Why is Silman not a GM? Even though he's my favorite chess author and have studied his books for years I just realized he is only an IM. It doesn't make any difference to me because I think IMs make better chess teachers (at least for me). I'm just curious.