The show is NOT shot in Washington DC, making practical locations difficult to find. Busey would say something on one day and Williams would respond to it 2 weeks later. So budget requires even great TV shows to resort to the evils of phone conversations. It's important to remember that TV has it's roots in radio, not film. The networks began on the radio, broadcasting radio shows.
TV shows are dialogue driven.
Movies have MUCH different roots. Movies began silent - telling their stories through pictures. Movies began as stories told visually and that tradition exists to this day. TV is about the dialogue, movies are about the actions. They have different roots, different traditions, different types of scripts.