Premium cable TV you mean? Cable was originally mostly rebroadcasts of transmissions that already had ads in it for people that couldn't get a signal.
Most media companies dream of having everyone paying a monthly fee instead of relying on ads. You have to constantly seek out people to sell ad space to and you're always at the mercy of the price of ads and seasonal changes. The usual issue is that people are totally unwilling to pay anywhere near what advertisers will pay to show them ads. Youtube's per-person income is low enough that some people will probably happily pay.