I don't think it's about being tainted. It's that there's a bunch of C++ code out there already in Production in a ton of places that doesn't pass those checks, and may or may not actually be safe. It would be a ton of work that may not produce any end-user value for any C++ project to switch over to that.

Meanwhile, Rust has always had those checks, so there can't be any Rust code in Production that doesn't pass them that would be painful to switch over.