The problem is that baseband or whatever drivers are made in kernel trees that are essentially forks of the kernel at a certain point in time.

This means that any fix needs to be backported to that special tree, irrespective of whether the Broadcom code is impacted, which may prove challenging when you end up having not just one but many trees, each at slightly different levels of outdatedness.

The approach clearly does not scale.

The solution would be for Broadcom to be diligent and forward port their tree to current mainline or current LTS at a minimum but they won't do that.

See how the RPi kernel is generally stuck at a special old version (e.g 6.6 for pi4, which is quite reasonably a LTS but then there's 6.12 as LTS already)