Maybe the difficulty of the game could be a factor? The PoKéMoN games have an incredibly easy storyline. Hell, you can get through it using just one or two PoKéMoN if you want. As such, anyone can beat it and come up with a decent guide for it (as long as they have the ability to type comprehensibly).
Unless you were talking about guides for EV's and stuff, basically things used for outside the main game and more in the metagame, then that would probably be because of the metagame's popularity, which is what VASM was talking about.