[tempestn]

It depends how you look at it. Once you've booked your ticket, United is better off if you don't take the last leg of the flight than if you do. Prior to booking, they would of course prefer you book the more expensive ticket. Forcing you to take the last leg is about encouraging you to book that more expensive ticket; it's not because they actually lost something when you chose to skip the final leg of the journey rather than take it.