The codebase is extremely shitty, instead people opted for complete rewrite.
There are several bad architectural decisions and when your architecture is wrong, the quality of the code itself doesn’t really matter (to be more specific, I was talking about architecture in my previous comment, not the code itself, I don’t know Rust so I can’t really comment on that).
To fix the architecture, major parts would have to be rewritten, almost making it a different codebase, because pretty much no part would be left unturned.