Thomas "Dreadflame" Sitch here. I worked with Todd back on Shadowbane and then later on Wizard 101, and built the backend server technology ("Tornado2 Engine") during my own independent game developer time. We're using that technology on Crowfall, which cuts off about 2 years of server development.
What happens in the background? It turns out, quite a lot. A production quality MMO needs to be able to scale up to meet demand. It needs to faithfully save, load, and cache persistent player data. It needs to distribute load as players come in, communicate with external systems (such as using your forum name to log in), it needs to withstand DOS attacks, and it needs to handle small failures (such as bad data or game logic) without taking down the entire system. The Tornado2 logic does all of this, plus a large amount of game code (such as inventories, equipment, loot drops, skill system, etc.).