WHY DONT PS3s PLAY PS2 GAMES?

ok we all know that the new ps3's only play ps3 and ps1 games not ps2 games, but heres the thing i dont get. you can make internal memory cards for ps1 AND ps2 inside of the ps3 hard drive, so why would they make the option for saving ps2 games on the ps3 when you cant play them on the ps3