can they simply fork?

Forking the Linux kernel will effectively guarantee that no one will run their software. None, but the most niche distros would ship it. If the Rust people are forced to fork, their time may be better spent contributing to Redox.

Why do people love Rust so much?

Rust makes it very difficult (but not impossible) to write dangerous code, whereas C pretty much guarantees you'll write something dangerous (and therefore insecure or buggy) at some point, especially in larger codebases, like the Linux kernel. Arrogant devs will defend keeping Rust out of the kernel by saying things like "write better code", but if the people writing kernel code for 20 years are still writing dangerously flawed code, it's safe to say that at a certain point, we need a better tool. That tool is Rust.

Rust also has very high-quality libraries that produce nicer finished products. I learned Rust because of clap and ratatui, which make superior CLIs and TUIs to anything else. Seriously, go use a CLI or TUI that was made in Rust. Try bat, a cat clone. You'll get easy, great command-line completions, easy-to-read help output, optional, beautiful syntax-highlighting, theming, etc. It's hard for me to go back to vanilla cat.

And I say all of that as someone that likes C. C is really fun, and it's a very powerful language, but it was not designed to be memory-safe. If it was, the people complaining about Rust would just complain about C too.