Sorry, but the learning curve of a programming language matters a lot. It's already hard enough for people to read and write code, so to learn another hard language like rust is not something you do lightly.

Rust is a cool language, but it's a cool tool, nothing more. I'd rather see the ownership process implemented in some C/C++ dialect. I'm not entirely sure, but I think that C++ concepts, in a way, have the same goals than ownership.

Safety doesn't always matter. It matters for a company like Mozilla and anything that's network/system related, that's for sure, but for games, I'm not so sure.

Also, statically typed languages that compiles to machine code are a niche now, new languages in that area don't really matter. You either have kernel code, or interpreted languages. A big quantity of C/C++ userspace code is fossilized code. Computers are quite fast for a lot of interpreted languages.