The inability of the monitors to tilt is probably due to how narrow the seats are that Delta used. There's hardly in depth to the seat back on these new seats and you need some to create space for the monitor to tilt. This is essentially the same seat that's on the MD-fleet and the CR7's after all.
All that said...how Delta could invest the money on monitors knowing they wouldn't tilt is a real head scratcher. People want monitors flush with them, regardless if they claim to have 60 degree viewing. You'd think this was focus grouped but then how could a focus group, a large percentage of, think tilt-less screens were great? It just doesn't make sense. Sounds like a major fail.