Because BN subscribers are hardcore UK boxing fans who are exempt from buying the fights. It's not a fair reflection on the legitimacy of the PPV without including them IMO. They pay for every fight on box nation with their loyal subscriptions.
There costs pay to the monthly costs of keeping the channels head above water, well that and loads of soft loans.
I reckon it must have done between 150k - 200k buys. There was a lot of hype and buzz on Twitter about this.