I think that happens because Kitty is a "waifu", you can see that in many of the writers that have self inserted as her boyfriend, even great critically acclaimed writers like Ellis who did that through Pete Wisdom. If they make her gay, she can't be a waifu for straight men anymore.
Gay men don't have that problem, so it's easier to let them be gay.
Honestly, I think it's a problem of the writers, not the readers. Many writers are in the age group that made them read the original Claremont run as kids, with Kitty as the young character for teens to self insert and fall in love with. Most modern readers are probably irritated by Kitty, or how she has been written the last years.