But someone has to pay for that extra capacity, if you have sufficient off peak work you can spread the cost to make it viable but if you only have a single trip in each direction that needs the extra bus and you don't have enough viable off-peak work to cover you need (taking a relatively low day cost for a bus) about 70 people paying £3 per trip (and school kids are often travelling on discounts so income is some cases may well be below £3 per person per trip) which is difficult to achieve. There are ways to massage these numbers, and operators may take different views on how to cost a peak duplicate depending on the nature of the work, to come out with a slightly different calculation depending on circumstances but at the end of the day even a dozen passengers left behind on one trip isn't going to be a viable demand to meet.