When you lose, your equity decreases 100%, when you win it only goes up 50%, you don't gain enough when you win to offset the possibility of losing, because there will still be three solid stacks remaing even if you double up.

On the flip side, SB has very little to lose pushing complete garbage, because you shouldn't be calling with anything but premium hands and he's far from crippled even if you call and win, while he's sitting pretty if he busts you (and gets the amusement of doing it with 72o as a side benefit).