While most of the rest of the airlines have reduced prices in an attempt to increase the number of passengers, Delta has done the opposite. Every time I have booked a flight in the last 4.5 years Delta has been at least 150% and usually tow to three times higher than other airlines for the same destination.
I am a medallion level flyer with Delta, but can no longer afford to fly with them.
Differing prices between airlines for the same origin/destination/dates are usually caused by availability issues, not structural fare differences. It may well mean that Delta is filling up before the other airlines.