If you think about it from Delta's perspective the streaming entertainment makes much more sense. They avoid the cost of putting a TV in every seatback, get rid of the annoying boxes under the seats, but can still give entertainment to everyone (or at least everyone who has a device of some sort). Delta can say they provide entertainment in every seat with a minimal investment in hardware and with minimal ongoing maintenance. Personally I think it is a brilliant business decision.

Plus it distracts from the uncomfortable seats, lack of food, poor seat pitch, etc. since we can now watch our entertainment from boarding through deplaning.