Originally Posted by ATOBTTR

You have to look at this from a larger network perspective. The NRT hub for DL relied on both O&D to Tokyo and onward connections on DL's flights to sustain all the flights into and onward from NRT. When NRT was the only option from N. America, all airlines were on an about equal footing in this regard. With HND being given a flew slots for service to some N. American cities, HND is now the preferred option for much of the Tokyo bound O&D traffic. Both AA and UA and their respective alliance partners still have a significant presence at both HND and NRT so they can still attract O&D and connections to/through both airports and sustain their operations. However, due to the few slots at HND that have been given to N. American carriers, DL cannot shift its entire operation to HND but to remain competitive at all in TYO, they of course have to take what they can get at HND with that being the preferred airport for most of TYO. Thus for DL, the O&D required to sustain their NRT ops is being syphoned away to their own flights to HND and also to the partner flights for customers who simply prefer the more convenient option of HND and are perhaps more tied to convenience or time-savings than airline/alliance loyalty.

Tokyo may still be an "important" market for DL, but it is becoming a spoke in the DL system, not a hub and the traffic that was going onward from NRT to other Asian destinations that have been cut can be funneled through other hubs.