Because the language of the week changes often, and learning can be done by solving the problems of today instead of rewriting software into a version that will never be used. I mean... who still uses all the rewrites to ruby?
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.
I ported DOOM to it. In 100 LOC. BTW it's just a a line shooting a ball of zero width, at another line. And there's some movement left and right. But not forward, nor backwards. So there's no real strafing. And the other line doesn't shoot a ball of zero width back.
I started reading hackernews from very old posts to new ones, so i'm still rewriting stuff to ruby, because that will definitely be the universal programming language for the future!
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.