When boiling point increases with pressure food cooked in pressure cooker should take more time as its b.p. had increased and it will take more heat.

But why is it not happening

The boiling point of water in cooker doesn't decide the rate(faster or slower) of cooking of food.

The temperature inside the cooker is responsible for faster cooking of food.

Steam have high temperature than water. So food cooks faster.

 

Boiling point increases when the external pressure applied is more.

Not the pressure created by the molecules of the same substance inside a closed system (like cooker).