How does a small group get politicians to pass laws to help them? It's pretty simple: some people care about people who aren't them.
I'm pretty plain vanilla as far as my orientation and family life goes, but I would never vote for a politician who advocated for any position other than full equality for LGBTQ folks.
4.5% of 301 million is about 13.5 million - and that's just people who would self-identify as LGBT in spite of it still being a problematic thing to admit to (we even have a word for it: coming out). Elections are decided by much, much, much smaller numbers than that.
(In comparison: that's more than the entire population of Pennsylvania).
PS: I certainly would be uncomfortable identifying as a Jew in an environment where people merely "don't mind all the jews and hebrews, but do wonder what's up with all the stuff". Just put in that framework to see what's wrong with your question.