The drive for reproduction is way stronger than the need for energy (sugar - ice cream).
You need to eat to not die before you need sex.
What I mean is that sex is easier to reach for than food when a person is bored.
Just like heroin is more potent than aspirin.
Also it has been proven that both sex and heroin stimulate pleasure parts of the brain.
Ever notice how folks have sex less frequently when they're in relationships and as they grow older? Where the opportunities for sex exist in multitudes? Yet they never stop eating. You can live without sex, you can't live without food. The drive for the two are not comparable.
But porn is easier...