Why would they care? The folks asking for this are a tiny (tiny) minority of the market.
Which is why they have a special configuration for that, sold to them by Intel.
coreboot was initially developed at LANL, a US Government laboratory. It's worth considering why that might be.
As for coreboot, keep in mind that it was originally developed long before the ME was a thing. IIRC the original motivation was that BIOS sucks. Which it does, sure, but that's orthogonal to the ME.