Your first mistake was trying to change your family. In any way. I can relate to you in that I’m the only liberal in my family, and it was deeply upsetting when most of them voted for Trump. I had to do a lot of work to separate their politics from our relationship. Their votes, values, and opinions have nothing to do with me, or whether they love or respect me.
It sounds like your family has been generally very accepting of who you are (not wanting to tell your grandparents that you’re gay is easily circumvented by you just telling them yourself), but they’d rather not discuss things that are upsetting. I can relate to that too.
I think you’re being way too hard on your mother, particularly since you mention repeatedly that you’ve never experienced any kind of abuse — you just want them to agree with you. They’re not going to. If it’s not possible for you to have a relationship with them unless they change, then I guess it’s good that you’re backing away from them. I just hope you realize this is completely on you, not them.