Video is a linear medium like audio, unlike photography or film. A film camera captures the entire frame of a picture in a single instant. But video was originally designed to be transmitted over the air. Images must be broken up and transmitted or recorded as a series of lines, one after the other. At any given millisecond, the video image is actually just a dot speeding across the face of the monitor glass.
Television is also primarily an analog medium.
The system we use today was established in the 1930's. Color was grafted onto it in the early '50s. The initials stand for National Television Standards Committee. This is the committee that established the standards for our television system. The problem is that NTSC is an analog system.