Yeah, that makes a lot of sense. If something takes a bit of work to join, it'll naturally attract only people who are invested in improving the community. I imagine new communities that get popular need cool people to get it started and keep the fire going. Not many people will know about it and it may be small, so there's a nice natural filter where only dedicated members self-select into the community.
Once it grows and offers more value, it becomes more visible and it spreads in awareness, so more people know about it, but then it's just as likely to attract low-quality members who don't really care about maintaining it. It's much easier to take for granted because it's just there and doesn't take effort to keep going, at least to a new member.
I think this is one of the things that I dislike about meetup.com. It's too easy to sign up for something and then not show up. It's a third party service, so you don't ever need to interact with a human being. If someone invited you to an event, it's a bit harder to bail on it, but if you just clicked a button to say you were going to go, it doesn't feel so bad to never show up. I think communities need an effort to maintain and a "member" putting in the work makes them more attached to the community. Showing up regularly is a kind of ritual, and over time, you become a true member of the community.