That's because the schematics are basically under heavy NDA. Designing a motherboard is basically impossible without heavy help from Intel or AMD and that is provided under NDA only.
That's why boardviews are so nice - they don't reveal *anything* about the actual PCB fabrication other than position of the parts and the logical connections between the parts (ie, which pins are on the same net); they are not *design* files, likewise schematics aren't truly revealing a lot either, certainly not enough that you could implement a clone for exactly the reasons you cite, there's simply too many other things such as firmware, routing and actual timing/impedence-control of the signals that go well beyond what can be deduced from the schematic and/or boardview alone.
If you look at common boardview files for things like Macbooks, all they contain is a long list of the following data tuple
{ position, side, part#, pin#, network name }
I had hoped that Framework would be a real change in the market but we're still locked out from really repairing those boards because there's no boardview access.
Sure, you can fix some things without the schematic and/or boardview ( they're two separate things btw ), but if you really want to be able to service machines that have been damaged you do need both in this day & age.
I've approached Framework a few times and it keeps ending up with a dead end when it comes to the boardview ( even through the conduit of Louis Rossmann to assist ). Basically, the whole repairability marketing tilt is little more than skin deep; they don't even have the rights to the designs to distribute the boardviews, of which I will point out are NOT the same as design files.
Physician: One upon whom we set our hopes when ill and our dogs when well. -- Ambrose Bierce
