EZE, rubbish pax yield, no need for F, competing against Norwegian, from a pax load point of view what it needs is a B788...BUT...loads of cargo which the B788 would never fit, so add this to the pax requirements of the route and what it really needs is a 3-class B772 to carry all that, which unsurprisingly is exactly what BA sends.
What IFE they are offering or how old the cabin is vs the flight length has absolutely zero impact on the decision making process, all that matters is fitting the right distribution of the 5 classes of freight namely F, CW, WTP, WT, Pallet class.