Why there is one fee for the whole order

The fee is charged once per order, not once per ticket. It is a fixed part plus a small percentage of the order, so when four of you buy together the fixed part is paid once instead of four times. The more of you there are, the less each person carries.

Most ticketing works the other way, with a full fee on every ticket, and that is the whole reason ours does not.

Whether you see it depends on how the organizer set the event up. Some events put the fee inside the ticket price, so the price you see is the price you pay and there is no fee line. Others show it as its own line at checkout, before the card is charged. Either way nothing is added after you pay.

Organizers keep what they price. No monthly fee, no listing fee, no charge to create an event. The rest is on the pricing page.