Google develops Android and thus is responsible for it's update scheme. They already changed it quite a bit in the last years with GSIs and Project Treble but there's still no real seperation that would allow the same drivers and hardware blobs to be used independent of the Android Version or updating the Android version without these needing to be included every time.
Their own phones have support for the mainline kernel. It is the vendors that dont want to upstream their drivers and produce half-proprietary garbage they dont publish, so nobody can update these devices.
But Googles decides, that that is possible. I fthey changed the structure to enforce a seperation there's nothing that would keep Android updates from those devices. Put all hardware and device specific stuf in a seperate layer and have it accessible to the updatable system. And it's not like these vendors have an alternative to go to
And there are Linux distros with rolling releases, where the drivers stay where they are and the OS around them gets updated without issue. I'm sure the smart people at the Android team could do something similar
The drivers are in the kernel, kept updated with every release. As I said, pixels at least boot with mainline kernel support, but the Android kernel is modded.
And then manifacturer use out of tree drivers as core part of their kernel.
Yes I know the manufacturers do, but there's no reason for the drivers to be replaced when the kernel is updated, you could hold them separately or reapply them after an update