It's all about killing the secondary market.
Venues, artists/teams, and TicketMaster feel they need a cut of the revenue if you choose to resell your ticket.
When you resell a physical ticket, the venue/Ticketmaster/artist/team doesn't see any extra money (the scalper gets their cut), but the risk if that you might be buying a fake or used ticket.
With e-tickets, you can "resell" them as 100% genuine tickets and Ticketmaster is the scalper instead. I suppose that becomes paying for a service, but I think it's more about making sure no more money is made on sold tickets.