The problem with lemmyrs.org seems to be that it is poorly maintained, still on Lemmy 17.4 and few moderators aso. Programming.dev otoh is very well maintained, well moderated and still not a huge centralized place. It also host many other interesting resources for programmers. Also, the structure of lemmyrs.org with many smaller communities doesn't work really well at the moment, it would require a huge number of users to avoid these communities being ghost towns.

[–] snaggen@programming.dev 8 points 2 years ago

In short, running an instance requires quite a bit of work, so having a really small instance might be quiet a challenge. Programming.dev is still niche, but large enough to not be a one man show.