The change had nothing to do with IBM. I know people view this with skepticism, but it's true.
The primary purpose of CentOS Stream is this: to allow a real community to be built around CentOS, where partners and users can contribute. With CentOS if you encountered a bug your only option was to file it against RHEL (not CentOS), wait for someone at Red Hat to get to it, then wait for RHEL to pick it up and release it. You would be very lucky for that whole process to complete within 6 months and if you're not a customer you probably won't be able to test a hotfix on your own systems.
Whereas with Stream: partners and downstream developers can file issues directly against Stream, and then contribute fixes directly to Stream, where they get QA'd in public and are added directly to the future release of RHEL. So Oracle Linux, Rocky, Alma and anyone else can actually participate in the process and contribute back instead of having to just take whatever RH throws over the wall.
However, the messaging and timelines around all of this were handled... not well, and some of the acrimony around that is reasonable even if the changes make sense.