For me, the license change upset me mainly for two reasons:
1. Many people had contributed their efforts to the Redis project for free - both in terms of code but also in advocacy, writing tutorials, publishing example code etc - and when they did that it was under the understanding that project would remain under the same open source license. It honestly felt like a betrayal of trust.
2. From a purely selfish point of view, my favourite thing about open source licenses is that they let me know exactly what I'm allowed to do and build on that software without having to consult a license. Licenses like the new Redis one leave me potentially needing to get my own legal advice depending on what I'm building on the software. I don't want to spend my time, energy or money on that stuff!
I do also see these kinds of license trends as harmful to open source generally. It used to be that you could pick an open source project and build a business on it and expect that the project would stay available to you under those well understood terms. That's not the case any more - not just because of Redis, there are a number of other high-profile license rug-pulling projects. I'm sad about that.
(And yes, I do understand and dislike the trend of businesses building on open source without contributing back. There are no clearly correct answers here.)