I haven't done ENOUGH consideration, let's put it that way.. Although I am a fan of your idea on it, Jyoliod. Even at that, I feel a way to explain a bit of it, is due to the saiyans being a massive warrior race, and being the quick to fight kind of people, a lot of them were killed off due to the immense amounts of fights they engage in. Though the planet has still survived, and saiyans still live in it, though there are much less than there once were.

Any thoughts on that idea?