Okay, so three things this topic keeps circling back to that I haven't properly addressed yet: the practical challenges of trying to write LGBT characters, the statistical probability of encountering a gay person and the politics that gets involved if you're LGBT
1) I think the root of the characterization problem with writing LGBT people comes from:
A) the fact that most writers draw inspiration more from what they've read than from reality, the fact that there already are so few LGBT characters in literature to begin with makes the situation something of a catch 22.
This also creates another problem where a gay couple is portrayed basically as a heterosexual couple: where the sex of the partners is homosexual but their roles are the traditional heterosexual one: one's the man, the other one's the woman. Anyone who's ever read any slash fanfiction can confirm.
B ) Socio-political problems. The "trying to represent these groups is terrifying" thing is real. It would be nice for all involved if it wasn't but it is. Sorry we're a wee bit touchy but when you have to fight simply because you exist while at the same time having to be nice most of the time because like it or not, how nice you act towards someone often has a very large influence on that someone's perception of gay people, it's exhausting. I think we have a right to be angry.
Speaking of "these groups", we should talk about intersectionalities, which I'll do in (3) to explain a few complicated things that aren't usually spoken of directly, hopefully it'll give you some perspective. I'll try not to make it too salty and you, I hope, will try to be nice about it.
(Oh, and yes, Brandon does not have the experience of a gay man, but last I checked he did not have the experience of being a woman or a crab woman either.)
2) Statistics, addressing the most frequent points:
A) Most cultures do not accept gay people, so the statistics of how many of us there are is going to be skewed. (And congratulations on discovering the meaning of the word "minority")
B ) Historical records are rather infamous for gay erasure. *cue historians saying "they were just friends" memes.
C) LGBT population cannot be compared with minority ethnic groups in terms of possible exposure, the latter are mostly localized, LGBT people live all across the globe, much to the consternation of both sides, but most unfortunately for some of us have to live in places like the Middle East or central Africa or Russia... which is a nice segway into:
3) Intersectionality, for those not into the social sciences, intersectionality can be described as the interconnected nature of social categorizations (race, religion, class, gender, sexuality) creating overlapping, interdependent and compounding systems of discrimination / disadvantage. The description is of course sanitized, lacking context of the horrifying experience of wading through this chull dung for the unfortunate many. (I won't get into it much, but there's plenty of YouTubers who're less shy about discussing these issues and are relatively easy to find due to how famous they are, if this is something you would like to look into further.) When this word is used, the accompanying discussion usually focuses on the "overlap/interdependent" part, what I want to give you some context for is the "compounding" part.
Religion, for instance, can be quite, quite hostile to gay people, the complications that arise from trying to address such a difficult issue is what I mean by compounding intersectionality, because irrespective of your stance on religion or homosexuality, any statement made addressing both in relation to one another becomes political. Your reactions can go, broadly, in three directions here: offense if your religious beliefs go against the acceptance of LGBT people, or "eep please don't rock the boat" if you're politically moderate and possibly even when you're stuck in a situation of compounded intersectionality because it makes it easier to navigate life, or "things cannot be changed for the better if you don't admit that something's wrong in the first place" if you're the campaigning type, etc. Unfortunately most politics take the first two options, and unfortunately for some of us, we're acceptable casualty for the sake of the ongoing social contract of niceness, which usually halts such discussions in any mixed setting. You have the option of ignoring these uncomfortable, inconvenient politics, for people like me, that's just our (sucky) existence.