tbh my feelings on leo have long been that he’s asexual (with a male best friend) - he has little romantic chemistry with anyone on screen, and the few blind items of women who have actually slept with him all say that he has little to no interest in sex at all, including that infamous one where he had to wear headphones and close his eyes during.
it probably suits both parties to have him “date” constant young models because in case no one expects him to settle down or go long-term (because he doesn’t have any interest to), and from their side they get a bit of press exposure and glamorous parties/holidays before the contract’s over. like you say, it doesn’t match with what we know of his personality.
that’s based on nothing more than reading blind items and stuff though