Good question and one that bears repeating. Because if you desire the aspect of free software or open source that is a level playing field, where no vendor has any special status or secret sauce, which in turn is what enables vendors to submit new features to a multi vendor codebase instead of maintaining private branches.

We learned this from X11 and the Unix wars, and history repeats itself in the countless free-core-but-proprietary-enterprise-features projects that never really expand beyond their parent corporation.

This is why trillion dollar corporations must not have special rules and the playing field must be even to any use, despite how unintuitive it may feel. Someone tried to codify it early as the first of the four software freedoms (the keyword being "anyone").

> Why is it completely unacceptable that those trillion dollar corporations (...)

The Redis licensing rug pull affects the whole community, not just strawmen villains. Random weekend warriors who occasionally spin up a container might not care. Anyone who trusted a FLOSS project to play a key role in their company's infrastructure will unavoidable have risk mitigation meetings where the name Redis is brought up.

Those corporations are direct competitors of Redis Inc. in the "managed Redis in the cloud" space. Would Redis be willing to sell licenses to them? Would they be reasonably priced?

It is not.

Why is it so unacceptable that they choose to collaborate on something completely Open Source instead (Valkey)?

They could easily just use the AGPL license, no need to pay for another one.