Does anyone honestly think the performances can only sell out because of scalpers willing to nobly buy large quantities for resale?

I strongly suspect they want it this way: promoters and performers like the aura of hard-to-get tickets, long lines, and sold-out shows. Plus, they can risk public derision and boycotts if they actually tried to sell at the market clearing price -- people are more tolerant of paying a big markup from some random guy for the exclusivity than buying it openly at the same huge markup from a faceless corporation.

all those other businesses add value to the supply chain. While ticket resellers can add value but when they purchase a large portion of the ticket supply they are adding little value.