They already had made a strong statement by choosing BSD when GPL was at their disposal. That is a much stronger statement than some blog post that reflects a momentary snapshot of their plans.

It is just that people don't hear what they don't want to hear. Every BSD or MIT is a loud and clear statement to deny the guarantee that derivative works will remain free and open.

People and companies are allowed to change opinions, why would anyone blame Redis or Elastic instead of Amazon for taking it all?

Because Redis said they would never do something and then changed their mind (which makes the whole concept of saying you will never do something useless), while Amazon never said they wouldn’t use open source software for free (which is their right).

I'd still trust more antirez than amazon as entities.

Never trust a company.

What does trusting antirez help me if he’s working for another company?

You're not arguing for the honesty of individual companies, you're arguing against the profit mechanism.