I have no knowledge, but would guess:

• building an app is harder than people think
• an opinionated community doesn’t generally help
• Java, eww.

PieFed seems to have taken the spot as well, mostly delivering on what Sublinks wanted to be but faster and better. Python is more attractive than Java even for the Rust haters.

Everyone is ok with Python. It’s a reasonable choice that’s well known, well understood and doesn’t have a lot of negatives. There’s a million libraries for it so it’s easy to get started and add support for new things.

I’ve never met a hobbyist developer who writes Java for fun. It lives in the enterprise world mostly, and not much else that I’ve seen.