The engine continuation here is 1.e5 dxe5 2.c5 6d6 3.fxe5 bxe7
Based on the engine line it looks like the engine just thinks blacks dark bishop is better for whatever reason and trading it off is the best idea. This wouldn't be possible if the bishop was on any other square.
One reason could be because your pawns are on dark squares, and if you trade off bishops you would have dark square control(I think this reasoning is correct, someone correct me if i'm wrong).
Another reason could be because you have a backwards pawn on c3, which is likely to become a target in the future. Trading off the dark square bishop would make it harder to target this weakness.
Some further analysis, if Qc8, then the best move is to retreat the bishop to d4. In this context, where you put the bishop doesn't seem consequential. Engines are dumb like that. In this position I personally would've just retreated the bishop to g3 or something.
Can someone explain why bishop to "b8" is the best move here?