Americans depended on the radio much more so than the television for information and entertainment in the 1940's and early 1950's. Then as more Americans bought black and white television sets and more programs were broadcast, the television got an edge. Much of early television was in the category of variety shows in which musicians and dancers could perform, not all that much different than stage shows, and then dramas, again not much different than what was in the theater.
For music artists who had hit records and live performances, television with its close up capabilities could be a challenge. Never was being able to project charisma to a camera more important. Many music artists felt self conscious and uncomfortable about the close ups. Some of them took to wearing dark glasses to hide behind.