Bishop exchange in Italian (Giuco Piano)

The problem is that the author didn't evaluate the follow up moves correctly and finished his evaluation of the position in a superficial way, the engine saw it a couple of moves deeper.

9-Bxc5, dxc5 and Bb5 (attacking the knight, the only defender of e5), Qd6 (defending e5) and Bxc6 leads to black having to recapture with the b pawn having 3 pawns in the C file like they mentioned.

After this Black has no good pawnbreaks which makes it very hard to make progress in the position, you are forced to passively defend which is even harder to do as a human!

I let the engine evaluate 8. ... Bb6 (allowing better pawn structure after the two exchanges) and 8. ... Re8 (protecting the e5 pawn to allow avoiding bxc6 recapture) and got +0.1 and +0.2 respectively which is marginally worse than 8. ... Bxe3 but within the usual fluctuation in an opening. So the conclusion is that keeping the tension on the g1-a7 diagonal is not a bad idea per se, the real problem here is the outlook of white enforcing bxc6, leaving the pawn structure on queen's wing completely wrecked. Thanks to all for the insights.

After Be6, White can take on c5 and e6. You will have doubled isolated pawns. Maybe that's why?