Thats a very simplistic view that doesnt take into account the sort of logistics that go into a big tour.
In places like Glasto its easier, as theyre not putting up any PA. But on their tour, the stage has to be built, the PA and lighting rig and video rig needs to be put up, its a lot of hard work. Those teams will have started work at 6/7 am the day of the gig, for it to be ready. It is, therefore, much nicer to be able to do a couple of dates at the same venue, as it gives the touring crew time to rest.
The artists arent the only ones working. In fact, they are the ones with the least amount of work, as they only have to show up to soundcheck, and then the gig.
They LX, SD and VD crews will have been there all day, setting up, and THEN doing the gig.
Dont forget that after a gig, on tour, you have to take everything down, pack it in the trucks, and move on to the next tour destination. It is seriously hard work.
It is wiser to have several dates at one venue at a time, before moving on.
Labour laws have changed since yesteryear. So touring is scheduled for the benefit of the CREW, not the fan. (obviously, if they know they can only feasibly do one show in any given town, as there wouldnt be enough interest for more, they do that)