I think you are right on all fronts, I noticed people pointed out the huge box office that Brokeback Mountain and other LGBTQ films achieved as well. And I don't think Billy Eichner had the leading man appeal/market clout to helm this, I don't think his love interest in it is well known either. The fact is that this film had far more promotion across social media of famous types than I have ever seen. The trailer has a few "straight people are dumb/lame" type jokes too which again, niche not mass market. I think Eichner is funny but he should have known this was a risk for all of the reasons you say, I am surprised it got greenlit for wide distribution, rom coms are not doing great lately and cinema across the board is really struggling as a result of many people taking economic hits the past few years (my household included). It's a weird time for movies for sure.