I don't know their motivations but mine would be:

1. Rust is a much more pleasant language to work with.

2. You can improve the tools, adding new features, fixing UX paper cuts etc.

You're probably thinking "you can improve the GNU versions!" and in theory sure. But in practice these sorts of tools are controlled by naysayers who want everything to stay as it was in the 80s. The sorts of people that only accept patches via git send-email to a mailing list.

Hahaha I just looked up GNU Coreutils and not only do they blame poor UX on the user ("Often these perceived bugs are simply due to wrong program usage.") but they even maintain a list of rejected feature requests:

https://www.gnu.org/software/coreutils/rejected_requests.htm...

And to nobody's surprise, to contribute it is git send-email to a mailing list.

Another maintainer and I follow issues and pull requests on a GitHub mirror. But email works fine for us and many other projects.

Regarding poor UX, it is difficult to dispute with that claim without a specific example. Note that a lot of the features we support are standardized by POSIX. Even if we dislike the behavior, it is better to comply with the standards so the programs don't behave differently than users expect. The sentence you quote isn't meant to put down users. These programs are often much more complex than meets the eye, and there are lots of common gotchas that people have run into (and will continue to do so) [1].

Of course we would love for these programs to be useful for everyone. However, feature requests are often incompatible with existing behavior, incompatible with other feature requests, or have existing functionality elsewhere. For those reasons we cannot accept every feature request.

[1] https://www.pixelbeat.org/docs/coreutils-gotchas.html

Have you used busybox? The BSDs? I'm not sure adding more features to coreutils is a major help, and given rust-coreutils/uutils has:

1) more CVEs between two latest Ubuntu releases than coreutils has had over the last 30+ year

2) managed to break security updates

3) is neither fully compatible with POSIX nor coreutils

I'm not sure why I'd ever use it? Sadly, projects like uutils have made me suspicious of rust projects, so unless I know that the project is well maintained (for which there are numerous examples, ripgrep being the obvious example, but newsboat, the various tools from proxmox, servo/firefox, and the pgrx ecosystem are ones I use regularly), it's a negative marker against that project.