My uneducated guess is that AA (a) sees the success (assuming it was successful) of EU-based airlines which started pulling content (e.g. basic fares) from the GDS years ago, and (b) they want to offer lower fares to more price-sensitive leisure travelers while gouging less price-sensitive business travelers. Ok. Could be a valid approach.

Companies are generally tied to using a big travel agency ("TMC") because they have to manage spend and must provide duty of care. That isn't possible if everyone books on airline websites. The problem with AA's move is that it puts their customers (companies) in the middle of a conflict between airlines and TMCs. Airlines want more flexibility to price than the GDS allows (fair), but TMCs aren't generally capable of doing anything with NDC content. TMCs say they don't want to build and maintain individual connections to every airline out there (also fair).

AA's success would depend on their ability to pull only content that's cheaper than the discounted fares that other airlines offer corporate partners (and thus maintain market share). And necessity breeds opportunity - eventually there will be so much demand from corporations to access lower fares that the TMCs will have to find a way to get the content back.

ETA: I agree - that Cranky Flier article sums it up pretty well.