Question about the daily puzzle.

Hello, I was looking at the daily puzzle and I'm wondering why the answer is what it is. Why after the move 39... b5 by black does white play 40. axb5? Why doesn't white play 40. bxa5? To me that seems the better move, as black doesn't get a passed pawn that way, while white still does and one that is further away from the black king.

lichess.org/training/WhD7K

bxa5 bxa4 b6 Kc6 Kd3 a3 Kc2 a2 Kb2 e4 Kxa2 e3 Kb2 e2 Kc2 e1=Q
Black wins

If we go as you say, 40. bxa5, then it's black's turn and black plays bxa4. There goes black with a pawn that can't be stopped.

Thanks for the replies, using the computer is a great idea!