Yes there is a contract inherited from CO that gives dTV full control of all in-flight entertainment on the 737 and 753 fleet (12 753s from ATA excluded from contract). This is why even the newer 737s have direct TV. It's also why the "dark" 739 fleet that doesn't have seatback dTV installed is still dark. UA is contractually not allowed to install any inflight entertainment (including wifi) that is not outfitted by dTV. This is also why there is a discrepancy in pricing for wifi. The new dTV-provided streaming for these "dark" planes is not yet ready, and UA cannot install its own streaming system as it has done on the other fleets.