Because if the rules were the same people would make fun of male pitchers saying they skipped around like girls when they pitch. Now, one could say that they skip around like girls when they pitch, but the girls don't actually skip around when they pitch. Gives the men a monopoly on skipping around, which is rare in sports these days.
ASA or what ever alphabet league in general. Men can step back, leap, and crowhop. Just curious why women have to have both feet on the rubber and cannot leap etc. Why the different rules?