DY includes more - bags, meals, seats etc when you book via a travel agency than when you book direct. Level/IB you have to pay for everything, including seat assignments in Premium Economy. PE on DY is vastly superior in room to IB, and I think 787 is a superior plane [seats aside] to the A330 for passenger comfort with pressurization/humidity etc.

Also since AA has pulled their previous exemption of OAK/LAX-BCN for credit, there's no incentive that way.