I wonder if we're perhaps getting our cause and effect mixed up here. I don't think it's unfair to say that the companion writing in this game is the best, most compelling writing in the game by a wide margin, compared to the main story. What if what we're seeing isn't a result of the general public just being dumb and horny, but rather them... meeting the game were it is, so to speak. They play the game and see that the character stuff is the most interesting and engaging and they think that it's because that's the part of the game that's meant to be important, the part of the game they're supposed to get invested in, and so they do get invested, and spread the game out to other people who enjoy that sort of game. So they're not disappointed by the poor main plot because they're coming at the game form the perspective that the main plot isn't really what the game is ABOUT, similar to how in Mass Effect 2, the main plot is there, but it's a vehicle to drive you to experience the various companion missions.
I don't think those people are dumb, but I've met the same crowds in the BioWare forums for the DA and ME romances, in the SWTOR subreddit a lot of posts are also about the romances. It seems to be one of the most popular features in crpgs and the devs cater to that. I personally don't care much - I'm not offended by sex, but I don't need it in my games. But I would like, if there would be a bit more balance between fixes for story issues and fixes for companion issues. So far it looks, like companion issues are the main priority - at least in my humble opinion. As I said, I love the game, but I think, it would be nice, if they stop catering to every romance whim and start looking into the story stuff. And yes, most companions are written very well, they have good storylines and you can luckily see them even without romancing them.
I am unapologetically one of those types that love having some romance in rpgs. pathfinder:wotr, swtor, bioware games, I love it. But what those games do not have as you've correctly identified, is an overwhelming focus on titillation and meme worthy focus on sex at the expense of a coherent main story. Arue's romance in WotR wasn't the main story. You could ignore it completely and get a very good main story experience. Having that added connection to the characters and world however enhanced the main story even more, as you started to think about things like "wait, if I go true Aeon, that means I have to..", etc, and that MEANS something. SWTOR always had great stories, and the romances didn't really have a large part in the story, they were definitely more side content, but they still enhanced the connection to the characters imo.
BG3, while it does enhance the connection to the characters, in my opinion, it does so in a very immature manner for the most part, and the huge focus on companions massive harmed the main story, and I won't even say 'imo' because I think it's clear that they simply stopped caring about the main story in Act 3. Instead of rewriting some things to make Act 3 better, we had bear sex memes, and fanservice rewrites.
I mean, the fact that Icelyn of all people is saying she's disappointed in Halsin's "romance" says a LOT. (no offence to you intended Icelyn :D)
(off topic, did you change your profile pic Fylimar? Or am I going crazy and you're someone else lol)