Because the media interest was amazing the year before Red Bull took over WRC Promotion?
ISC/NorthOne were pretty hopeless, and RedBull have been extremely disappointing. They've had 3 years, and I don't think things are generally better. There is a clue in the job description; 'Promote'. Take this weekend; GB is a country that has very little mainstream interest - so RedBull should be making an effort to sell the event/ sport. It's not rocket science.
As with a lot of promoters, they sell TV rights, and don't do the hard work of promotion.