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. The above is also the reason why you always see people sitting in restaurants talking on TV, but it's something to avoid in a film script. Something that's perfect for TV might be the worst thing you could do in a film.