Developer and volunteer time and attention is a finite resource though. Effort that was spent on open software that's now spent on proprietary software is less effort being spent on open source. Furthermore if you're now expending effort to fork something - in this case possibly many things - thats effort you're not spending on what used to be your higher priorities.

Yes forking might in some cases be the only option, but it's not easy and it's not cost-free especially when the code is still available 'for free' (warning: many actual freedoms not included).

Nothing is free. There is no entitlement to benefiting from someone else's investment in software. I don't see why future Redis development or whatever can't be taken proprietary.

Yes, you could make a license that precludes it, but if you insist on copyright assignment then you'll always get the right to re-license anyways.

I understand nothing is free. Creators and owners can license their software however they please. Their freedom to do so is not what is under discussion here. The vast majority of the code I’ve ever written was proprietary, but I’m very proud of the roughly 10k lines that is open source. We’re just having a debate about pros, cons and possible consequences, which I think is perfectly reasonable and legitimate.

It might be worth collectively paying someone else to do it.