John
The government spent around $7 billion on the Comanche before it was cancelled. Bell probably assumed something from that program could be salvaged and the original 360 proposal included the ducted tail fan to meet anticipated RCS requirements. Once it was recognized that low RCS was incompatible with the pusher ABC configuration, the final requirements for RCS on the selected prototypes were relaxed to allow the Raider to compete. With that requirement no longer a constraint Bell wisely reverted to a conventional tail rotor to save cost, save weight, improve reliability, and reduce program risk while still meeting the final program requirements.