The X-Men were originally a metaphor for the US Civil Rights movement (and, to an extent, LGBT people), back when a metaphor was about as daring as people were game to be.Oh these people aren't PoC's therefore the analogy doesn't apply.
What fucking difference does it make? Racism is racism period.
The makers of the X-Men films decided to have almost no black people, and totally no LGBT people, in a franchise originally about the oppression of black and LGBT people. I'd also note there's at least 4 major characters in the franchise that, presumably purely by chance, are played by LGBT actors.
(I believe Mystique might be bisexual in the comics, but there's no evidence of that whatsoever in the films)