Rate this hypothesis. Pre-porn era, a man with good enough visualization skills will find it less necessary to date women.

This is because good mental imagery is almost as good as the real thing in terms of quality (maybe 70% as good?) but it's 100000000000000% better in terms of customization (the girl can look however you want, be whomever you want, the situation can happen exactly the way you want it)

Therefore, if your visualization skills are good enough, there is literally less of a physical need to have sex.