I've written some tools like this; some released, some not (mostly because unfinished). The problem with "merging it upstream" is that it's just a lot of friction. There are also some ideas I have and having my own tool gives me the freedom to explore and experiment without worrying too much what other people think or compatibility.

And then there's the language choice, as well as code quality. I don't really want to start a huge discussion about this, but it should be pretty obvious that many people are more comfortable and productive using languages that are not C, and that some of these tools don't have the best C code you can find.

A lot of "Rewrite in Rust" (or Go, Python, what-have-you) isn't really about the "Rewrite in Rust" as such, but rather about "Rewrite so I can play around with ideas I have".

Also see my comment from a while ago when someone asked "why do this when $other_tool already exists?": https://github.com/arp242/elles/issues/1#issuecomment-216855...