Tarrasch defense with 6. dxc5 Chesstempo database gives white over 65% in all the variations after 6. dxc5 (130 games with both players 2200+). It has been used by Anand and Ivanchuk. So why the main line 6. g3 is way (2800+ games with both players 2200+) more popular where black scores much better?

It has to be because of black's preparation. But what should be the correct response? I don't see one using the database. Nor can I find one using chess engine.

[Event "?"]
[FEN ""]

1. d4 d5 2. c4 e6 3. Nc3 c5 4. cxd5 exd5 5. Nf3 Nc6 6. dxc5 d4 7. Na4 Bxc5 
( 7... b5 8. cxb6 axb6 9. e3  )
( 7... Bf5 8. e3 d3 9. Qb3 )
8. Nxc5 Qa5+ 9. Bd2 Qxc5 10. Rc1
6. dxc5 is just a good move, and you cannot really hope to refute it. It was given an exclamation mark in Grandmaster Reportoire 10 by Ntirlis and Aagard, and their main line starts as in your diagram.

Moves such as dxc5 were underestimated by older theory because they were thought to give the initiative to black. Nowadays with computers we can analyse more concretely and see if blacks initiative is something to be afraid of or not. In the case of 6. dxc5, the analysis seems to suggest that white ends up with a small advantage.