There were very many open pull requests from the community that were all invalidated overnight for something that same community was assured was merely an experiment.

The normal process would be "hey, this experiment is going well, we've made this plan, come help us shake out the new codebase for the switchover in X time." None of that happened. There wasn't even an announcement, just a silent commit that trashed hard work from hundreds of community members.

Developer community. "Open source" historically implied that an interested developer might hack on the code and submit their changes. But if the entire code-base is rewritten by the maintainer every year, then there's no developer community.