I think the thing is (a) TM's take of the sales, (b) TM's owning the scalping/auction system post initial sale, (c) TM's exclusive hold on Box Offices at venues & (d) TM's propensity to drop fees as line-items with on-the-nose labels on the tickets they sell.
Basically, they've abused a monopoly position, and painted a target on their backs by trying to nickle and dime folks.