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.
There were hosting services for forums in which free or cheap tiers were on a subdomain like that. I think what you’re asking is the inverse though, e.g. mastodon.alostinquirer.org. I find that odd too, as it creates a weird situation if the person hosting it wants to use different software for the same purpose, e.g. Pleroma or Firefish for microblogging instead of Mastodon.
I probably should have adjusted the examples as like metalbulletins.org to better describe what I was trying to ask.
It’s not strictly the explicit software as part of the address that I’ve found odd, so much as the blending of the software in the names, but I think generally it comes down to the same basic point being made in the different comments concerning domain registration and management.