Reasons boys like breasts:
- Wanting what they do not have.
- Cultural emphasis of breasts and cleavage being attractive (not all cultures view breasts as sexy).
- Oedipus complex (granted access at birth and then denied for years).
- More entertaining than a stress ball.
- Their sensitivity to touch and the reactions playing with them causes.
- CuriOSity - wanting to explore what is covered and glimpsed but rarely bared (varies by culture).
- It adds to the appeal of the S curve in art of the female.
Is a reason really needed? It all boils down to a matter of preference. Why do many people like the color blue? Simple - they find it pleasing for any number of reasons. The same thing can be said of breasts.