This is a common use for residential proxies. Ticket touts buy use of the infected users to make requests to try beat restrictions on access from data-centre hosts or high-volume access from and other hosts, to increase their charge of getting valuable tickets for later resale.
A number of backdoored (by the creator, by someone cracking into their source repositories, or in this case by buy-out) free browser extensions, VPN apps, and such, turn the user's machines into a proxy like this.