I'm not sure if this went away or if it was never an option, but I'm wondering why Avios & Money is not an option for domestic flights within the U.S.
From the Conditions of Use, it says it's available on American Airlines. I don't see any specification that the flight must be international (especially since it's available on domestic flights in Europe):
Avios & Money section:
Available on one-way and return itineraries on British Airways and franchise operated flights, Air Berlin, Aer Lingus, Alaska Airlines, American Airlines, Finnair, Iberia, LAN Airlines and Royal Jordanian only. Codeshare flights are excluded.
https://www.britishairways.com/en-us...ditions-of-use
Is this something that might only be available over the phone?