Though it sounds like a genius travel hack -- sometimes saving up to 80%, according to Zaman's post on Reddit -- “hidden city” booking's frowned upon by businesses. Orbitz, for example, expressly prohibits “hidden city” bookings. And if frequent fliers are caught in the act, carriers can delete their accounts and ban them from flying in future. In addition, luggage may not be loaded off a flight until it's arrived at its final destination, making it even harder for passengers to pull off this trick.
The lawsuit stated that "hidden city" travelers can “cause disruptions” to United’s processes, including the airline’s “ability to estimate head counts” at the airport gate, and even affect “mechanical tweaks, such as variations in the amount of jet fuel needed for each flight". That's a complicated way of saying airlines want to squeeze every last penny out of you, and they'll cite legal and technical tangents to do it.