My hot take is that CNCF, when you look under the hood, is nothing more than an avenue to promote your project. Once you get people to know about it, it's kinda dangerous to leave it there (other companies may try to change its direction) and I can see why Synadia wanted it back.
They were the majority of the commits so there's no risk that someone would change their project's direction.
Ockham's razor tells me that they realized too late that they don't have a viable business model, the money dried up and that's why they wanted to make it proprietary.