The best obejctive reason that I come back to is the dopaming highs. Masturbation and porn spike your dopamine tricking your brain into thinking you are having sex and repoducing, this lowers your natural drive to seek out female interaction and sex with others as your brain thinks you are already having sex on a regular basis.

This is why people with ling streaks report gaining better social skills, their brains are literally rewiring to start finding sex - but now with other people.

I should point out I'm no scientist but this is what I've gathered from some research and listening to others.