This is true for basically every budding community. "Rustaceans" writing tools for writing rust, in rust, seems like a gimmick, but every language goes through this period. JavaScript is probably the single biggest offender I can think of, but other examples include rewriting Vim plugins in Lua even though neovim supports vimscript, rewriting literally anything in Go, rewriting python libraries in Julia, etc.

I don't think the example of rewriting python in Julia is the same. Most python libraries get re-written (or implemented) in a faster language. If your choice is rewriting in C++/Fortran, or writing rewriting in Julia, The Julia version will be way nicer to use, and will probably be faster than calling the low level library from python.

You're talking about rewriting performance sensitive code when it makes sense to do so. I'm talking about rewriting random libraries because developers like to wallow in their tooling.