well the service charge originally was a surcharge added onto tickets to cover the fees and make some profit for the ticketing company. So essentially you were paying a fee to cover the software used, the phone operator and the overall convenience of not actually driving to the venue and buying tickets in person... and this made sense...

Unfortunately over the years that service charge has morphed into other thing... While it is true that some of the service charge money goes into funding the costs of selling you a ticket (staff, software, servers... ect) it also became a very strong revenue stream and a way for ticketing companies to "lock in" certain venues or promoters... here is an example with fictitious numbers and fake company names:

Ticketlord wants to be the official provider of tickets for the Madison Cube Garden, so they make an offer: Instead of charging the usual $6.00 service charge and cover our fees and make some profit, we will now charge $10.00 and give $3.00 back to the Madison Cube Garden.

Suddenly, this venue signs an exclusive deal with the ticketing provider to ensure more revenue and it gladly allows the ticket provider to look like the jerk.

Promoter deals are the same, however in some cases (AAA Artists) the performer makes so much guaranteed money or a very very high percentage of the ticket price so this is the only way promoters can guarantee themselves a revenue stream.

i could go into a lot more details but that should give you a good idea for now.

Edit: a few typos...