Can someone please organize an AMA for each of these vendors' product managers? I have the feeling they live in a different world and it could result in interesting discussions.
Other reason is that kernel requires some minimal level of code quality and many of the closed source ones are basically "the minimum to make the customer use case work"
Yet another reason is just not wanting to bother with more than bare minimum for chip that will be in market few years and replaced with something newer
I think this is the real, actual reason. Having worked in embedded for a long time, the coding horrors are endless and routine. There's no way 99.99% of embedded software would ever pass the kernel's strict code quality standards. It's easier to just ship a "bastardized" (as others here are calling it) patched kernel.