This is a tremendous amount of cope. Implying there are Lemmy users just lining up to contribute PRs if only it wasn't written in Rust. Give me a break!
If someone was competent enough to author code that's fit to pull into a project like Lemmy, they're more than capable of translating those skills to Rust. No language seeing modern significant use is so esoteric that a reasonably seasoned developer couldn't make something competent in it within a week of starting to learn its syntax. Maybe a day, even, if the language you are trying to learn is highly similar to one you already know.
Sure. Which is why I would only make this distinction in a place where I can reasonably expect people to know better. Like, perhaps, a niche community on an experimental social media platform dedicated to programming.