The others serve more routes than New Delhi station. CNB and ALD effectively serve as the hub for 6 routes, BZA for 5, ET for 4. KYN and DR serve the formidable Mumbai suburban railway along with the mainline traffic. While NDLS has a lot of originating trains, the others have a substantial number of passing trains.
In addition, all the other stations see very heavy freight traffic too, which is comparatively far less in NDLS station.