Zeke,
Airbus had never thought before QF72 that switching OFF a faulty ADR was a top priority, they have changed their mind since, at least for that type of ADIRU.
Switching OFF a faulty ADR, in the UNRELIABLE SPEED INDICATION / ADR CHECK PROC has never been a top priority. It had to come up at the right time, but not before a thorough analysis by the crew was performed.
As you mention the first two lines of the UNRELIABLE SPEED INDICATION memory items, note that switching OFF a faulty ADR is NOT one of these items.
Actually it is mentioned only on the second page of one of the longest procedure figuring in the Quick Reference Handbook.
Applying the UNRELIABLE SPEED INDICATION memory items was considered enough to maintain a safe conduct of the flight, just enough to grab the QRH and read through that long abnormal procedure where, eventually, the faulty ADR would be switched OFF.
I would guess the QRH was not open on the table for a minute when the AOA protection decided to take control ...