This is from that Guardian article posted by hyg above:
“Because Channel 4 has a smaller reach than BBC1, the new Great British Bake Off is doomed to be a comparative ratings failure. The new version would do very well to draw half of the average 13.85 million weekly viewers who watched the final BBC series last year.”
So if the new series only gets half the viewers it did on the BBC, where have the other 7 million gone? And why?