There’s absolute mass quantities, as Beldar the Conehead might say.

It’s easy enough to guess that plenty of people just grabbed a community name in case they might find it useful one day, but I’m guessing plenty of others legitimately started up a community, put some effort in to it, then ultimately got discouraged and abandoned it. A big part of that likely due to not being able to attract many subscribers and contributors.

Personally what I’ve found is that if you really want a community to grow, you need to seed it with content on a regular basis; preferably daily. Posting bots are probably a good way to help with that, altho if the sub looks like it’s little more than bot posts, I don’t think users will be inclined to post or comment much.

What I haven’t quite figured out myself is how to incline users to post on their own, but hopefully with time that issue will kind of resolve itself due to sheer user count.

Btw, see here:
https://lemm.ee/c/fedigrow