Isn't crystal lang trying to do the same thing? Why not join forces?
Nope, Crystal is a statically-typed language with distinctly different than Ruby semantics that features Ruby-ish syntax.
Sorbet is an optional static type system for Ruby.
They aren't trying to do the same thing. One is trying to appeal to the aesthetic preferences of developers who like Ruby with static typing, the other is trying to enhance the Ruby ecosystem with static typing. There's only a superficial similarity between these things.
Just like in C, you have trivial, nontrivial, complex apps, then there's still a long way before production OS kernels at the extreme.
Many advanced libraries don't use metaprogramming much, and even if they do, it can be often made either more explicit or shifted to compile time.
Edit: The downvotes are interesting since the portability claim comes from my experience doing just that.
Having said that, such optimizations are indeed possible and we are already thinking about how we can use the type information we have to that effect. There are still many things that need to line up for that to be a thing, so we are not expecting any new developments on this soon. But this is a very exciting direction for our Ruby Infrastructure team at Shopify.