Because the company that makes them, 3DFX, is out of business, which equals no drivers, no support, no forthcoming games. Plus, the 3500 just plain sucks and has crappy drivers that will never be updated. The 4500? I didn't even realize they got those to the shelves before they folded. Get a GF2 MX if price is an issue. If not, get a GF2 Ultra or GF3.
LJ