The BBC coverage has almost certainly allowed the festival to book bigger acts whilst paying very low fees. WIthout that I don't see how people like Stevie Wonder, Elton John, Rolling Stones, Jay Z etc. would give it a second thought.
It has probably also led to influencers etc treating it as such an important event to attend which has arguably ruined it somewhat but kept it relevant.
Without the BBC it probably would have kept going at a smaller scale, but the festival would not necessarily have been able to put money into things such as the SEC, Arcadia etc. so I think it's a double edged sword