Different Prices for the same thing??

I am intrigued to know why the prices vary so much on club sites?  Surely the cost of electricity, water remains the same all year?  The wardens are paid the same all year, so how can a site vary so much?

Broadway at the moment is priced at £17.70 for two adults and a pitch, the most expensive it is during the year is £28.20 that is £10.50 more per night what exactly are we getting extra to justify that price hike or is it purely profit making which was I thought not what the club was about?

I'm sure this has been asked before but as a fairly newcomer I was just interested in logical reasons for it