My understanding is that there was some trademark silliness around "open compute", and AMD decided that instead of doing a full rebrand, they would stick to ROCm but pretend that it wasn't ever an acronym.
>>atq211+(OP)
Yeah it was due to the Open Compute Project AFAIK... Though for a little while AMD was telling me they really meant to call it "Radeon Open eCosystem" before then dropping that too with many still using the original name.