Example: As a user of (original) CentOS, you discover a bug. Where do you report that bug? The Red Hat Enterprise Linux bug tracker, because CentOS is just a clone and the community has no real ability to fix things. Then what? You wait until a Red Hat employee gets around to looking at it, and then wait until the next patch release which might be up to 6 months away.
Now repeat with the new model.
As a user of either CentOS Stream or one of the RHEL clones such as Alma Linux, Rocky Linux, Oracle Linux, etc. you discover a bug. Where do you report that bug? The CentOS Stream bug tracker, upstream for RHEL and thus also upstream for all RHEL clones. CentOS Stream is a community project, so the community (including yourself, and including maintainers for Alma / Rocky / Oracle Linux) can actively contribute to and drive the fix onwards to completion and test it afterwards, wheras before it would sit in internal nightly builds for a few months.
Both the community and Red Hat benefit from aligning incentives that way. However, I understand why there was a lot of frustration about the way it was announced and implemented. It could have been handled better.
disclosure: I work for Red Hat, but not on anything related to RHEL or CentOS Stream.