I wrote extensively in Ruby but for Rake - using Ruby as a build system. Can't say I liked the language although it was okay for how we used it. We have 20 sub projects with some very complex build targets and dependency scanning going on and the Rake syntax was okay. Personally I think its biggest shortcoming was the documentation was very poor and stuff like gems felt primitive compared to other package management systems. One thing I liked from the language was blocks could evaluate to a value which I really use a lot in Rust too.

I think if I were doing an acyclic dependency build system these days I'd use Gradle probably.

As for Rails I expect failed to catch on because even compared to Python, Ruby is a slow language. And Python isn't fast by any stretch. Projects that started with Rails hit the performance brick wall and moved to something else.