I can’t imagine why you would expect drivers to be mainlined by a vendor.
Because I was a Windows kernel developer for Intel. It was standard practice for us to give our reference drivers to the OEMs to deploy with their devices, while we worked with Microsoft to inbox the reference drivers. This was part of the value of the Intel IP.
That’s not the norm.
It is the Norm for PCs. And we are talking about, "Laptop manufacturers making handhelds, leading to cost cutting from a resource perspective." We aren't talking about ARM vendors making 1 off devices.