Like what has been alluded to, there used to be only a few channels of TV, they probably didn't come in very well and the stations went off the air at night. A stereo, on the other hand, could play hundreds of songs all day and night if you wanted it too.
I think once cable became mainstream there was more entertainment for those who weren't musically inclined or who just wanted something they could turn on and play. For those who liked electronics or to tinker computers were the latest thing.
Chad