Two reasons I can think of-
I have been doing some research and it is fairly obvious that Jesus didn't actually have much to say on the subject of sexuality at all.
Aside from the "let he who has not sinned cast the first stone" story, which some scholars think is a later accretion, there is only one sermon quoted.
That is, that a man who lusts after the wife or betrothedof another obsessively, has already committed adultery. I take this to mean he is looking at her a s a sex object, not a person, and disregarding her commitment to another.
All the other references to sexuality in the New Testament come from Paul and others.
I have to ask, who is more important Jesus or his later followers? I would guess that Jesus didn't think that these questions were of any great import. He was more concerned with people living by the two Commandments he gave.
If those busy quoting scripture stopped to listen to themselves, if I am right, they are committing blasphemy, by making Paul et al, greater than Jesus ( who, remember, is God). hopefully if they keep ranting no one will catch them out, and they will not have to deal with being exposed.
Secondly, the Churches seem to insist that a marriage has to be consummated in an act of heterosexual penetrative intercourse, which reduces the woman to an object to be possessed. Any marriage definition which differs, reduces the power of the patriarchal institutions over their female members, by indicating that men are not superior to women , by divine right.
Hope that is not too obtuse, I could probably rave on for pages.

Karen.