Why not maintain it rather than writing something new? Open source is frustrating

The community has taken it over as far as I know. Looking at the github there appears to be some active development still. https://github.com/rethinkdb/rethinkdb

"Is RethinkDB dead?"

https://github.com/rethinkdb/rethinkdb/issues/6747#issuecomm...

TLDR: They are hoping to announce a revival in the near future.