A full-service TV station is required to deliver its highest quality signal to its city of license, regardless of where the transmitter is located.
In the analog world, the signal degrades over distance and the highest quality signal, called city grade, covered a relatively small area, which is why the transmitter was located fairly close to, if not in, its city of license. The grade A signal, still a good signal, covered a larger area, and the grade B signal, which could be marginal, covered more area.
In the digital world, the signal is either there, or it isn't, and if it's there, it's a clear signal, better than the city grade analog. So now a transmitter can be farther from its city of license, and still provide a high quality signal to it.