I could try to give a reason why since I think I'm part of that precentage on the PS3...
But it doesn't really matter...
The PS2, just like the Wii, got tons of "non-quality" to somewhat "shovelware" games. The leading console always gets the most games, simply because dev's see it as the easiest place to sell a crap game because of the figures.
4 ≈ One