Because they touch themselves at night
I don't know really, some other countries have much worse age restrictions, like Germany for example, or Russia, even Ireland.
LA!
Some good games (without pictures, sorry) are:
Bio Hazard Battle - Megadrive, one of the best shooting games on any platform, very cool design and music.
Dragon Ball Z: Supersonic Warriors - GBA, a contender for best DBZ fighting game, even over hyper dimension (that's a maybe), very close to the actual show.
Space Gun - Arcade, a complete rip off of Aliens, but who cares? It's a helluva good lightgun game.
Gundam Wing Endless Duel - SNES, this is one of my favourite fighting games ever, and I've played millions.