Because American gamers tended to be pussies back then, and games had to be dumbed down for them. Working Designs was all like "f*ck you, we're better than you" and made games harder instead of easier. Also, there was often the issue of censorship... some things that fly fine in Japan don't fly here, and vice-versa. Cosmic Fantasy 2, for example, got Babette's middle-finger scene edited when it came to the West, and Mortal Kombat was cleaned up when sent to the East.
