I'll lay it out in detail so it's more clear: TicketMaster sold the original ticket to the scalper. Then the scalper listed the ticket on TicketMaster's secondary market. Then I bought the ticket on TicketMaster's secondary market and TicketMaster collected a $50/ticket fee from me. TicketMaster also collected a fee on each ticket the first time TicketMaster sold those tickets to the scalper.
TicketMaster also charges the scalper a fee to list the ticket, so TicketMaster actually made more than the $50/ticket fee that they collected from me.
It's also possible that the ticket was sold on TicketMaster's secondary market several times before I bought it on TicketMaster's secondary market, which would allow TicketMaster to collect many fees on the same ticket.