I think network effects have a lot to do with it. If a language has a small ecosystem, it's less attractive for new developers, so the ecosystem stays small. That said, I think the Nim ecosystem might be able to achieve a critical mass of useful libraries soon and break out of that cycle. There's been a lot of good work done in the UI and web domains in the past year, which is such a large market that even capturing a small portion would bring a lot of developers into the ecosystem.