In the French line 6. bxc3 Ne7 7. Qg4 O-O 8. Bd3 why 8. ... c4 is not played?

I'm looking at the French line 1. e4 e6 2. d4 d5 3. Nc3 Bb4 4. e5 c5 5. a3 Bxc3+ 6. bxc3 Ne7 7. Qg4 O-O 8. Bd3 and I wonder why 8. ... c4 is not played here at high level:

The most played move is 8. ... Nbc6, but this allows 9. Nf3. It is too late to play 9. ... c4 because now white has the deadly move 10. Bxh7+.

If after 8. ... c4 white wants to remain active they must play something like 9. Bh6 Ng6 10. Bxg6 fxg6 11. Bd2. I wonder what's wrong with this position for black, so that it is avoided at high level:

Well, one problem would be 11. Bc1 intending 12. a4 and 13. Ba3. 

Another problem is after your 11. Bb2 white has the very natural plan of h2-h4-h5 Ng1-f3-g5 then sack sack mate. That might not work against a comptuer, but it could be jolly tricky for black to defend against. 

Black's light squared bishop is pants and it can't go to g6 via d7 and e8 because there's a pawn there already. The other role it might have going to a4 via d7 leaves e6 chronically weak. 

I think it's just a bit harder for black to play than the other lines available. 

I think the overall strategy is that black operates on the Q-side, to offset white's attack on the K-side.  c4 locks up the pawns on the Q-side and lets white stabilize the Q-side. Since dxc5 gives white such weak pawns, black can delay playing cxd4, just threaten it.

The moment when Black takes or locks with his c-pawn has to be timed perfectly, or the center just resolves itself in the center and lets White throw everything at the K-side (h-pawn, rook lift, knight jiggling in...)

Have you considered 9.Bg5, I wonder ?

Releasing the tension is a bad idea. If not Bh6 Ng6 Bxg6 Bg5 intending h5 and g4 then you can just bring the bishop back to e2 and start the pawnstorm anyway. Or you can even sac the bishop and start the pawnstorm. Or you can play Bxh7 and storm you have the activity to do so. It's just ridiculous. 

@iluvzmetuna

9. Bg5 in which line? Please give the full line. After 8. ... c4 if 9. Bg5 then 9. ... cxd3. 10. Bf6 looks scary but there is no mate. The problem is that it takes time for white to work their queen to h6 and when the queen is there they still have to do something about Nf5 which on the one hand discovers the bishop's attack on black's queen ( supposing that it is still on d8 ) but on the other hand attacks the white queen on h6. White has to play g4 to avoid this and black has time to slowly get out of trouble with something along the lines of 9. Bg5 cxd3 10. Bf6 g6 11. Qg5 Re8 12. g4 Nd7 13. Qh6 Nxf6 14. exf6 Nf5 15. gxf5 Qxf6. After the dust settles white's structure is completely disorganized now it is black who will go after the vulnerable white king:

I'll show you some lines one sec.

Can you find a line for black after Nf3? I'm having trouble doing so. Ng6 is a crucial move and by the time you play it white has time to play h4 and such and so the bishop being trapped doesn't matter. I've actually seen people sac the bishop so they can develop more pieces. Black's queenside is sleeping peacefully. There's no way he can defend the vicious attack with his queen blocked in.

Actually, 14...Rh7?? is a blunder. After 15...fxg5?, White can play 16. Qxg5+, winning on spot.

See? I didn't even see that, but it's there. Don't play c4. It's definitely too dangerous.

It might be dangerous, but it isn't a losing move...

Show me a line in which black holds and I'll agree its not a losing move.

Actually, 11...Nf5?? is the losing move!

nice analysis, watcha. i hadnt gone that far, but i had 2 other subvariations in mind. i might post analysis later. 13.Qh6, no I don't think so.

I love how you have no clue about the position and yet you act like you do. That won't make you any friends, sir. In any case, try this line:

Wow, you're funny! It seems to me that YOU are the one who's clueless about the position!