There are so many hardware certification programs out there, why doesn't AMD run one to fix this?

Create a "ROCm compatible" logo and a list of criteria. Motherboard manufacturers can send a pre-production sample to AMD along with a check for some token amount (let's say $1000). AMD runs a comprehensive test suite to check actual compatibility, if it passes the mainboard is allowed to be advertised and sold with the previously mentioned logo. Then just tell consumers to look for that logo if they want to use ROCm. If things go wrong on a mainboard without the certification, communicate that it's probably the mainboard's fault.

Maybe add some kind of versioning scheme to allow updating requirements in the future