Babysitting, as I used to do it as a teen, is not a career and does not require special skills. Families and parents look after each other and children all the time without training and pay, you don't need certificates and so forth to be a good trustworthy person who would cope reasonably well in a crisis.
The higher the standard required (DBS, childcare quals), the higher the price, the more it is seen as a specialist skill set, the more that ordinary people can't actually afford it any more. Who can afford £50 for a night out on top of actually paying to go out?! Only pretty wealthy people, I don't believe anyone I know (and I know mostly professionals) is paying this regularly any more, we are all in belt-tightening mode and that's more than the cost of the take-away we could have in instead.
Now, that's the market- if people want to pay professionals to do this in their spare time, in the belief they are better than a 16 year old down the road, that's their perogative, but it's all the perogative of others not to want that level of service or of pay.
My friends/other parents mind my children from time to time, or take them out or even have them to sleep over, and I don't consider that I require a DBS check/training/huge amount of relevant experience, just a bit of common sense and my mobile number.
Now I have read this thread, though, I'll be telling my dds' to definitely enter into this lucrative market when they get older, there's no point in cleaning/serving in a shop/delivering newspapers/working as a waitress if you can sit on a sofa, do your homework, chat to a child if they wake up all for the same price an hour or even more!