How come my PS3 doesn't support PS2 games?

Before i played MGS4 i wanted to play 1, 2, and 3. I played MSG1 and when i put MGS2 i got a message saying PS3 isn't compatible with PS2 software?!! How is it possible it supports PS1 games but not PS2 games?!?

MGS= Metal Gear Solid
8 answers 8