It's this mindset that make people care less and less about people wanting support in this situation.
You know what... I'm going to address this a bit more in depth. You are not an ally. You are not a hero. You are not a savior. You are absolutely 100% part of the problem. You THINK you're one or all of those previous things because you like to tell yourself that you are. You WANT to be those things, but you don't want to have to prove it or stand openly for something. You want to be able to jump into a conversation and go "Oh yeah I totally support trans rights!" but you don't want any even slight inconveniences that would come with any of those tags.
Well, this is the real world and this is not how it works. If you want to seem supportive of the LGBTQ+ community, you have to actually know what it means. You don't need to know everything, but you need to be at least willing to put in some effort to educate yourself or others. If you don't know where to begin it's 100% fine to ask (again, neither the original person being quoted, or you did ask. You said "The polite thing to do would be to explain it", implying that if a trans person doesn't feel the need to play someone's personal tutor, they are the ones that are rude).
No one owes you an explaination on their personal life choices.
So get out of here with this "It's this mindset that make people care less and less about people wanting support in this situation." because you never cared to begin with. At best you pretend to care, but you quickly dropped it and shown your ass and we're all better for it. Knowing someone is a fraud makes it much easier to not waste time on you in the future.