I think they are still mostly for that even now.Are glory holes a real thing in hetero spaces outside of porn and erotica? I always, maybe incorrectly, thought they were for discreet gay hookups back when people had to hide themselves more
I believe that there are "adult cinemas" and the like that have them set up in a somewhat less improvised way, that women can also use.
Apparently, some people really want truly anonymous sex (or oral, I guess) with whomever happens by. Goodness knows why; it makes me shudder.