The fourth finger being shorter it is often easier, when using multiple fingers - as you might prefer to do for a bend of a tone or more - just to use the 3 longer fingers when you're bending. The tendons of 3rd and 4th are such that they are not totally independant, even the great pianist Chopin bemoaned that his little fingers wouldn't obey him.
Personally I use my pinky a lot but rarely for bending.