I mean, you can create a GPL fork of the Rust coreutils if you so please. Or you could do a rewrite in any programming language of your choice and license permissively.

In any case, I profoundly cannot bring myself to care about the fact that you can legally create a proprietary fork of permissively licensed FOSS. I don't think it's right to impose any restrictions on what people can do with software/code, which of course conflicts with the fact that other people can take your code and restrict what other people can do with it. So choosing between copyleft and permissive licensing is a balancing act of that contradiction. I don't think it's wrong to end up on the side of permissive licensing.