To the best of my knowledge the ARM ecosystem is an absolute pain to work in, you can get Phone/Tablet SoCs painfully encumbered with out of date drivers and binary blobs. Or you can get enormous server processors that will cost $1000+. There just isn't much that's suitable for making a desktop or laptop that would meet Frameworks markets expectations.
And even Microsoft is dealing with pain points like Qualcomm he, few, and drivers actually breaking the spec and causing problems in servicing and supporting the ARM based devices.
Meanwhile properly SBSA compliant chips aren't targeted at mobile market at all and thus often lack certain features or are too energy hungry.
