I guess boxing is probably not something that subscribers are mentioning when leaving. Sky Atlantic doesn't do big viewer numbers but it attracts a different sort of subscriber than the one Sky normally gets.
Boxing does pretty good in the ratings, especially when the fights are in the UK. You'll usually find boxing in the top 10 listings for the week whenever there's a proper fight on. The K bros are pretty popular as well, getting around 200k viewers per fight and 300k when the replay is added.