Mojo is designed to be very fast to compile, so many decisions were made to keep the core language simple, one example is in `where` clause, the checking there happens entirely in the parser. It can be stupid in situations where other languages are smart, and make you explicitly do checks that could be inferred in other languages. But on the other hand, it can be very fast since it doesn't have to do all the complicated resolving.
Another reason is how LLVM is used, Modular found ways to parralize LLVM code generation by introducing novel techniques that'll likely become a lot more popular with other languages.
What techniques?
https://www.research-collection.ethz.ch/entities/publication...
C# compiler is also fully multithreaded since the Roslyn rewrite in 2016.