The BBB is useless for literary fraud. This has been proved many times over, and not just in the case of PA.
The BBB considers a matter resolved if the business replies at all -- even if it's a tone letter.
The interaction between a publisher and an author is considered a business-to-business relationship, not a business-to-customer relationship, so lots of the legal safeguards that consumers expect don't apply (even though with PA the authors are the consumers). And it's hard to get law enforcement interested when the individual losses are small.
White collar crime in general is hard to prosecute.
PA is relying on authors getting disheartened and going away rather than embarking on a long, expensive, and potentially risky lawsuit.
But ... balance that with the fact that every time that I'm aware of in which an author has brought PA to arbitration, PA has lost. And arbitration doesn't cost as much as you might think.