sure, I'd be glad to.. .thanks for focusing on the topic.
LGA-IAD is a much smaller market than DCA. even at DCA, DL is consolidating flights between JFK and LGA to DCA, probably to free up a slot here and there for new service to someone else's hub.
DL has regularly reduced flights to both DAY and ROC in part to free up capacity for increased southbound flying which is where the revenue increases.
DL does connect some traffic thru LGA. Given the slot controls, it makes more sense to free up capacity for the local LGA market rather than push connections thru LGA.
ATL and DTW serve the purpose well.
Also, there are strong rumors that DL is close to loading a number of schedule changes in LGA that will involve larger planes which will free up some of the large RJs for use elsewhere on DL's network. Larger planes also keep competitors trying harder to keep up with DL and the advantage DL has at LGA which has created a halo effect at JFK.
It also highlights that DL very much has competitive strategies in place to maximize the use of its assets including at NYC.
DL's capacity and network both at DCA and LGA and throughout the US will be larger by next summer than it is now or what can be seen by these schedule changes.
Guaranteed.