Oh, let's just go ahead and make a S.W.A.G.
Could it be that he just "too nice"? IOW: What she was missing was someone being mean, over-bearing, abusive, and rough.
In spite of the "sexual revolution", more women than will admit are attracted to the A$$holes of this world.
It is a fallacy that the choice is between "nice" and "abusive". A characteristic that seems to attract women is being civil while it being clear that you will not tolerate being messed with. Referring to the movies, "Pee Wee Herman" nice will repel women, while "Bruce Willis" assertiveness will attract.