Originally Posted by Mesabah

At high density airports, a certain amount of slots are allocated to small aircraft by the FARs. To maintain those slots, mainline will have to operate a jet that has 55 seats or less. FAR 93.123 This is probably the main reason regional jets still exist at Delta.

Delta acquired that NY market share in a series of deals, the most recent being the slot swap. Those are worth billions to the company, they aren't going to give them up. Getting rid of 50 seat RJ's would cost them a ~40% reduction in market share. Not to mention the ability to cancel RJ slots during IROP for mainline schedule integrity.