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)
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"
Or they didn't want to commit to the extra shows until demand was clear