The reality is, most cable channels had ads from day one. Less ads than most broadcast stations (which made up most of the channels you had on cable at the start anyways) but still a lot of the first cable-only channels had ads from the start. WTBS had ads on cable in 1976. MSG/USA had ads on cable starting in 1977. CNN had ads on day one in 1980. MTV had ads on day one in 1981.
In the '00s they still had no real ads, only promo spots for mostly other Disney shows on the channel, and the occasional tie-in with some other Disney property. I think today they have some normal ads but I'm not sure.