Yes that's a fair point, although Taylor Swift is somewhat of an exception/corner case. Some of the huge acts do sell cheaper than market rate for other reasons, but most of the events they sell for are not.
It's also worth noting that sometimes things change after prices have been set. For example, a baseball game in which tickets were sold but now there's a lot of attention/love suddenly and unexpectedly on the team (maybe they just pulled off a big upset or something) so "market rate" for tickets jumps much higher than what it was immediately before that when the tickets were sold. They weren't originally trying to price lower than market rate. Also the pricing they do for market rate is calculated to optimize for maximum revenue which includes some balance of selling max number of seats but only until the delta of additional sales means a net loss of revenue (i.e. you can sell every seat for $1 but that would make a lot less money).
