And why do you assume that 90% is side eyeing. I feel like you're projecting.
I went to every single midnight showing of the new Star Wars movies, starting with TFA, in full cosplay.
And i was being side-eyed at like hell. And so were the LotR fans during the Hobbit premiere.
Funnily, during our 'watercooler' talk, the day after "Rogue One" released, a colleague of mine asked me "did you go to the midnight screening? How was it? Buddy of mine went - said there were a bunch of weirdos dressed up as some of the characters." - "yeah, about that ..."
Again, it's people just caring less about what others think, because they find support and validation through other means than the 'offline' social circles of the 80s and 90s.
But outside of cons, people still find adults who dress up - outside of carneval or Halloeen - hella weird. And i can't blame them.