The most important thing a campsite offers over wild camping is a shower. So if you can find somewhere to get a shower eg sports centre, service station etc then wild camping would be fine.
And knowing that you can settle down for the night and no one is going to tell you to move on. Or find that your cosy camping spot is a favourite for local doggers.
I'm wondering how many gyms, sports centres and service stations allow you to just wander in and have a free shower.
I totally agree that all most solo campers need is grass, toilets, showers.
And campsite owners need to pay people to cut the grass, clean the toilets, run the reception, pay to heat the water, pay for the water, light the campsite etc etc etc. And that's not counting the initial capital costs and the cost of having to refurbish - which I guess you'd need to do every ten years or so.
I'll bet that right now bretonbikes is doing the sums to try of work out how to make it work economically.
Tempted to open a new thread asking for suggestions, creative and otherwise, for sources of easily accessible showers. But for now will ask folks to post them here.
I remember staying at a campsite in Le Marche that was run by an old widow, and the guy who had taken over the bar was telling me about the problem they had with campervanners sneaking in for showers. This is people driving around in vehicles that are worth £30,000 and up (maybe they've spent so much on the campervan that they can't afford showers I don't know). I must admit find something equally odd about people who are travelling around with a couple of grands worth of bike and camping equipment obsessing about paying a tenner or so for a campsite, and doing mad stuff like cycling until it gets dark and then having to move on before it gets light. (If you're going somewhere where there are no campsites or places to stay for miles and miles then that's another matter).
I know 'wild camping' sounds very romantic, but is it really just a posh euphemism for sleeping rough? Something you might have to do if you don't have the money, but otherwise why would you?
[EDIT: I wouldn't mind betting that a typical campsite charges less than most people posting on here earn in an hour (OK before tax)].