ATL is a fortress hub for Delta, and by extension, Skyteam. So the DL/AF/KLM can charge whatever they want and take the profits. I think DL has something like 80% of the slots at ATL.
It was the same for CLT (Charlotte) and AA being a former US Airways hub. AA owns 90% of the slots and makes huge profits there. Business travellers need the schedules and the companies pay for it.