Fair point Julie, but the club has to show a profit in order to survive. I have been on CCC sites in October half term - when you'd think they might be a bit busier - and have been one of five units. For many of the sites, with limited hardstandings, it would not be commercially viable to remain open all year.
There are far more all year sites now than when I joined 16 years ago, and I suspect that they will steadily extend the dates of more sites - but only if there will be sufficient numbers of units on site. There is a risk of site fees for only a few units not even covering the cost of the warden, let alone other running costs.