I think hive is alive and well, but I do agree that a lot of people have left. Onboarding/retention requires a lot of things to do and I do agree that dead projects are a problem. I have seen quite a few die because the people who were in charge just went inactive.
Unfortunately, we haven't really discovered the concept of decentralised work organisation. Most Hive projects are one man shows and when the guy gets tired, the project dies. We need to come up with new ways of organisation for a new economical reality.