Pretty much what is says in the title. Redis had been using the BSD-3 license for years to encourage developers to write code for them for free and now they've gone and switched to some custom proprietary license in order to secure their theft of the labor of everyone who has contributed to the project over the years. It's the same age old story.
A harsh, but important reminder to never write code for projects with these weak open source licenses. These licenses ONLY exist so that your labor can be stolen, either by them re-licensing at some point in the future or other companies taking it right now. That's the only reason they use BSD/MIT-style licenses.
As an aside it's a shame we're stuck with the GPL given the person who wrote it.
This is because of Broadcom's acquisition of VMWare. The company behind Redis got acquired by VMW back in the 2010s.
Broadcom is busy fucking everything and everyone they can, they do slash and burn style licensing where they fuck everyone who can't migrate off the software of the company they acquired.