Why is Be6 a better move than Bh5 in this position? Original position:

After Bh5 (move I think is better because of the threat to the queen if pawn moves):

After Be6 (move recommended by the engine):
Not only do you lose a pawn as previous answers told, but there's a strategic idea behind this too. What characterizes the position you gave is that it has opposite-side castles. On this positions, players try to pawn-storm their opponents and break their opponent's king position. With Bh5 you are giving your opponent the chance to start a pawn storm with tempo, which means you are basically allowing him to make his desired moves "for free" and succeeding easily on his plan.