Buncha reasons:

1. We have a lot to do that is specific to our system. Designing a "better" note-sharing protocol isn't a burden we need

2. Nostr is good! And has lots of clients and a decent adoption curve.

3. I think our tech can actually fix a lot of problems people have with Nostr relays. Good opportunity to introduce ourselves to a community with a positive contribution

4. Plunder should be viable as a "backend" personal API for anything you want to throw at it. Gobbling up existing "Earth data" and remaining compatible is part of the goal (vs just reinventing everything on the inside and not being able to talk to Earth)