Which is the result of how bad dependency managment is outside (i.e. DLL-hell).
Pretty much all other use cases of build.rs can be sandboxed. Well, there is sqlx that wants to connect to database at expansion time to compile check-queries (yew).
Although I suppose that's still doing a lot of shenanigans at compile time. It could be sandboxed pretty well (theoretically). I'd hate to give it up completely though, getting a compile time error when SELECT query params or return values have type mismatches is extremely nice.