Doug Parkers entire flow scheme was designed to limit costs. There is no other reason. The current flow system is a management creation, APA had no say in the matter. The company already had all the scope relief they needed so there was nothing to negotiate, American simply instituted the program.
As negotiations go on the standard reply from management is that they don't need to increase wages at the regional level, our pilots have the "flow to mainline." This is Doug's way of heading off a bidding war for talent at the lower level of the industry, the regional new hire.
From the posts, it doesn't seem to be working as well as planned but then again neither does AA's performance on many other metrics, vis-a-vie United and Delta.