Marketing 101. I don't go to concerts often, but there was one last year. Tickets for the thursday show were sold out within minutes, but oh look, they tried Really Hard and revealed they were going to do an EXTRA show on the Friday!
(they already had it planned but wanted to make sure the first show on the less popular day was sold out first)
Would you care to elaborate on what you mean with concert fatigue? I've never heard of it and you're talking about it as though it's something that is so common, it is implied to be known.
Logistically, it is complicated to do that unless it is a small venue and you are an indie band.
It takes a lot of planning, contracts and advance payments to make a reasonably big show to happen. Larger venues are usually booked with months in advance, and most things you pay in advance are not refundable.
I often see ads on Facebook for products where it says "selling out really fast" or "first batch already sold out" type of thing and my first mental response is "okay, I probably won't be able to get one then, I'll wait for your supply chain to catch up to the demand"
(they already had it planned but wanted to make sure the first show on the less popular day was sold out first)