Owen, did you read the article? The route was getting binned in two weeks. That would strongly suggest to me that it was either not making any money, or the money if was making was considered not large enough to justify the route continuing. Now, if they're being given £3m a year to keep it going, one could surmise that figure is around what it takes to make it viable.
As AerRyan says, it can be full every day of the week, but unless the yield is sufficiently high, then it'll be scrapped.