I read recently that for some men, sex is fast because they grew up in an environment where, for lack of better phrasing, they could only pleasure themselves “quickly” in the bathroom during adolescence. They sort of got used to getting off fast and it carried on to real relationships.
That said, I can remember, in my younger years, being with other guys and having marathon sex where neither wanted to finish and it would take hours and hours…trust me when I say that when we finally did finish, it was rather spectacular.