Because I know javascript a lot more than I know Lua (and I suspect given js popularity, a lot of people are in the same boat). Yes Lua is easy to learn, but it's still different enough that there is friction. The differences also aren't just syntactically, it's also libraries/APIs, and more. I also don't have any need/use for Lua beyond neovim, so it's basically having to learn a language specifically for one tool. It's not ideal for me.

But the people who did the work wanted Lua, and I have no problem with that. That's their privilege as the people doing the work. I'm still free to fork it and make ruby or js or whatever (Elixir would be awesome!) first-class.

i’ve written probably north of a million lines of production js, maybe around 100,000 lines of production ruby, and about 300 lines of production lua. lua is a fun language and i think a much better fit than JS for technical reasons (who has a js engine that is both fast and embeds well? nobody), but i am certainly more productive in those other languages where i have more experience.

lua array index starting at 1 gets me at least once whenever i sit down to write a library for my nvim or wezterm.