It’s a thing. Sometimes they’re just there with friends, which is fine. Sometimes they don’t know it’s a gay bar; not every bar with a heavy queer crowd feels like a “gay bar” to some people. Often, they’re women who just don’t wanna be hit on by creepy dudes.
Usually it’s not “tourism”, though. People don’t, like, wander in to watch The Gays. They’re just there to drink or hang out or talk to a friend or something. It’s pretty normal.