It seems to be more language focused than hard to PR against the main repo.
Java is much more widely known than Rust, which means a much larger pool of developers. I never contributed to the original Lemmy server because I couldn’t wrap my head around a full production scale rust project. I’ll very likely contribute to this because I work with production Java code daily. Im sure I’m not the only other dev who has run into this.
Also maybe there’s just too many disagreements with the Lemmy owners, who are a bit extreme for a lot of people.