1. Backwards functionality costs money, and they can't afford to increase the price any further. With microsoft cutting prices all the time, they needed to keep up with the costing, and some things needed to go.
2. The PS2 is still selling relatively well for a 9 year old console and its profitable unlike the PS3, which is selling at a loss. If they put full BC on the PS3 now, they would see PS2 sales die down along with profits.
3. They're on a wait and see basis, probably through this holiday season, waiting whether PS2 sales will die down completely. Unlike microsoft, who turned their backs completely on the original xbox, sony still sees life in the PS2.
4. PS2's fully advertised backwards functionality came with a rapid decline of PS1 sales, which was ok since the PS2 had virtually no competition on its time period. Nowadays, however, PS3 is in third place so they'd rather have two consoles out there selling individually.
5. Lots of people don't know a thing about backwards compatibility and majority of them already own a PS2 already so they could care less about it.
so yeah, basically when the PS2 finally stops selling consistently, i'm pretty sure they'll put BC on the PS3. until then, with all these reasons and others combined, there's just no reason why they should.
