Pretty sure this is around forcing the pace on NDC adoption, which means that the main corporate agents, all of whom are doing NDC, will be covered in the approved list.

You have to view this in the context of the monetization of AAdvantage and the desire to make that a big income stream in itself. NDC enables an airline to target individual members with individual offers on the far side of their indirect channels, including with dynamic pricing created for that individual and no-one else (in principle). That can include non flying products. The changes to AAdvantage regarding rerouting benefits and so on are designed to make being an AAdvantage member more likely, thereby increasing the overall pool value. NDC gives access to that member to a rich and diverse ecosystem. If you view it in that light these odd changes start making sense.

See: Airlines - Wakeup and Smell the Money (traveldatadaily.com)

Having non NDC channels operating in parallel potentially provides arbitrage opportunities and also slows the pace of adoption. There are probably legal issues in preventing ticket sales by non NDC agents, but not offering benefits is likely to be more palatable.

Quite what this means for those of us who are members of other FF programs flying AA is anyone's guess, but the logic is we lose benefits also as time goes on. Unless we play fancy footwork with the assigned FF number after being rerouted, we already have fewer rerouting options when there's disruption.