OP you said: "when I have been on hols and seen the clubs some children are hooning around and there does not seem to be much control and some children look lost and sad."
This is an important point - for most people who are happy to use kids' clubs in principle, it will still depend on the quality of the club in question AND on how happy their particular children are there.
For example we have used kids' clubs only where the carers are all trained to British standards, and care ratios were at least as good (and for some age groups, better) than required in UK childcare - in fact DD ended up with one-to-one care whenever she was in kids' club last time! But we chose the holiday partly based on that, and would not have gone somewhere with lower standards if we planned to use the kids' club.
Also I think most parents would see if their child likes the club, and then remove them if not. We definitely hung around lots to make sure they were happy, in fact often when we went to pick up DS he asked to stay longer. However there was one other small boy who we often saw crying for his parents (and being comforted by the staff - they did their very best but he just didn't settle), if he was mine I would certainly not have left him there and think most people would not have either!
As for wondering whether kids in the clubs are in childcare at home - well I wouldn't be surprised if the clubs have a higher ratio of children who have had some childcare, but not necessarily because those parents "don't want to spend time" with their kids - it's also likely that children who are used to spending some time at nursery or playgroup are more likely to be happy to try out a kids' club, whereas those who have never been without their parents are more likely to get upset and not be left.
Wordfactory - you are forgetting age differences again, seeing the sights is all very well with older kids (if they don't refuse because it's "too booooring"
) but with smaller ones, it may be just too difficult and impractical (and exhausting - not a holiday!) to do that every day.