Why did Rush stop doing his television show?
As he has said many times, TV is a group operation -- producers, directors, camera people, writers, meetings, meetings, meetings ... Radio is just Rush and the golden EIB mike. He chose wisely.
Unlike radio, Rush was totally at the mercy of whatever stations wanted. Most of the stations did not have him in prime time, but usually between 1 and 3 AM when there is almost no audience whatsoever. He did not possess the clout like Leno had at NBC or Letterman at CBS.