It's either LLM or "<existing software> written in <languge of the week>"
It's usually to help teach them the other language.
The rewrite part makes it easier for observers to learn and compare/contrast techniques in different environments for themselves.
Why this would ever be criticised, I can't imagine.
Even emacs was rewritten to rust ( https://github.com/remacs/remacs ), many hours were spent, and the last actual code commit was 5 years ago.... why not spend that time by making the "normal" emacs better? Or make something new in rust?
Well, it's actually just a hardcoded slideshow of E1M1 while something vaguely approximating the main riff of At Doom's Gate plays inconsistently in the background, but you'll have to watch all 15 excruciating minutes of this poorly-narrated Youtube video I'm linking to figure that out.
But it's the spirit of DOOM!!!
/s