They will ship images using a probably old kernel with various patches and drivers which may not be in suitable shape for simply including upstream. The vendor

They will ship images using a probably old kernel with various patches and drivers which may not be in suitable shape for simply including upstream. The vendor may ship this initially, but often won't work on upstreaming the changes or porting to newer kernels, so you end up with devices stuck running forks of old kernels unless somebody takes the kind of effort discussed here to upstream the changes.