Some people don't like Rust language, its eco system and community and the MIT license at all. Combine them and replace core functionality of a popular distribution, that is enshittification for some. Even though the Rust programs are compatible.
I don't mind MIT license and even do like Rust. But my personal problem with this decision in Ubuntu is, that these Coreutils tools in Rust are not proven yet and finished with 100% bug for bug compatibility and feature parity. So this is a premture decision in Ubuntu for my taste.