Comment by const_cast

> I'm interested in why C++ was chosen for this?

For the same reason C++ is chosen for a lot of projects. Probably the authors have a lot of experience in C++.

For an exceedingly complex and large project, you really want to choose a language you're very proficient in. Like, years and years of experience proficient in. If you don't have the experience in Rust then you don't have it. And, Rust is really the only other language that can be considered here. Swift, C#, whatever, are just a tad too high-level to write an engine in. At least, ergonomically.

I looked at the source code briefly and it's very high-quality code. Writing good C++ is hard, harder than pretty much any other language. It's modern, it's consistent, it's readable, and it's typed well.