I'd say lack of libraries, lack of tooling and lack of jobs/mindshare.

I would love to migrate essential libraries, and work on it full time, if there was a mentor, and some decent donation

So would everyone else, but that's the chicken and egg problem. Most languages that succeed these days have some major organization to kickstart them (Dart, Go, Kotlin), or some killer feature for a specific niche (rust, elixir). Crystal has neither, it's just a nice language.