Why should it be popular, it's missing so many things to be popular.

For example we're passed v1.0 and they keep breaking APIs.

https://crystal-lang.org/2021/03/22/crystal-1.0-what-to-expe...

> After this release, everyone can expect that, at least for any future 1.x version, your code can still compile and work without any significant incompatibility. Language and standard library features won’t be removed or changed in any way that could prevent existing code from compiling and working. The built-in standard library will continue to be enriched but always with backward compatibility in mind.

And yet 1.2 breaks many things.

Anyway it's not a language that will be mainstream because they don't have the resources to make it serious.