It kind of makes me think of how odd it would have been if many of the old forums named themselves like bookclub.phpbulletin.com, metalheads.vbulletin.net, or something.

There's nothing wrong with doing that, obviously, but it's struck me as another interesting quirk of fediverse instances/sites. Generally as soon as you visit them you can tell by the site interface or an icon somewhere what software they're using.