There is no evidence that cutting coverage in rural areas will reduce prices elsewhere.

The Canadian situation is bad-to-zero coverage in rural areas and the world's most expensive cell phone service (think of plans that charge $10 CAD per GB of data) in developed regions.

The money that Canada's two cell phone networks didn't spend covering rural areas didn't reduce prices; it disappeared into shareholder pockets.

Because you don't want to increase the class divide between rural and non-rural areas. Or maybe you do, but most of us don't, and you have to conform to our values if you want to live with the benefits that a society of those values have produced.