https://github.com/JuliaLang/julia/graphs/contributors
https://github.com/crystal-lang/crystal/graphs/contributors
Also, there's a lot of stuff that Julia has which Crystal doesn't (and vice versa since they focus on very different domains)
And the answer to that is that the semantics of the language were designed from the start for efficient JIT'ing. Thanks to the language design, Julia can get close to C performance with a comparatively simple JIT approach (resolve types, compile a function statically with LLVM just like C, then use multiple dispatch to select the right function at runtime (simplified, yes, but roughly like this)). Compare this with all the tracing JIT heroics that Javascript implementations or PyPy pull, while still getting performance far from what Julia achieves.
The crystal guys should have but their effort into nim or something like it imo
https://en.wikipedia.org/wiki/The_Art_of_the_Metaobject_Prot...