Why should they lose money GUEST,guest when most camping-only festival goers are quite happy to pay £5-£10 per night per person. This is additional revenue (if they have the space) and not a loss leader.

A good example of where this really does work is when Moor and Coast provides camping for non-season ticket holders at the Community College during the Whitby Folk Week Festival.
Their charges add up to £10 per night per person and no one complains because they are just so grateful that someone has taken the initiative to cater for droves of fringe goers.
Because of their not insubstantial efforts this makes a massive contribution to the well-being of the festival in terms of its overall welcome,acceptance and inclusivity of ALL festival goers.
I really do feel that this makes a big difference and that is all I am trying to say.