I understand that, but that is not a reason for allowing your opponent to promote, anymore than you would let him capture one of your Bishops with a Pawn (which would also give him a Bishop for a Pawn, if the Bishop was protected). In real games there never are any promotions 'early in the game'. At least not any where the promoted piece is allowed to survive. And there certainly will not be more than two. So if you want a Bishop to be available early in the game for the one-in-a-million case that someone would be allowed to promote and would want one, you might as well make it available in unlimited supply. How many games would have more than 2 promotions in total anyway? Usually the first promotion decides the game.
I understand that, but that is not a reason for allowing your opponent to promote, anymore than you would let him capture one of your Bishops with a Pawn (which would also give him a Bishop for a Pawn, if the Bishop was protected). In real games there never are any promotions 'early in the game'. At least not any where the promoted piece is allowed to survive. And there certainly will not be more than two. So if you want a Bishop to be available early in the game for the one-in-a-million case that someone would be allowed to promote and would want one, you might as well make it available in unlimited supply. How many games would have more than 2 promotions in total anyway? Usually the first promotion decides the game.