This is a little off topic, but NYC has 5 daily frequencies to Tokyo currently. So does Chicago. LAX has 9 frequencies, and SFO has 4 (plus 1 from SJC). Doesn’t it seem a little odd that NYC only has 5 daily flights? Shouldn’t there be more? This is why I think United will maintain EWR-NRT if they’re awarded EWR-HND.
5 daily is more than enough for NYC local demand. That said, to be honest, I was surprised that DL did not bid JFK-HND as its #6 "throw away" proposal instead of HND-HNL #2. The danger was, I suppose, that if they were awarded it, they would have to fly it, and the P&L forecast was obviously deep in the red. NW tried it (NRT) and failed. DL tried it (NRT) and failed. AA tried it (HND) and failed. The journey is long enough that a loyal DL customer traveling NYC-HND is not terribly inconvenienced by making a connection in DTW, and can depart/arrive from DL's closer-in LGA hub. Still, they are the only major player without nonstop NYC-TYO service on their own metal or jv partner.
Geography does not favor NYC, whereas LAX, ORD, SFO all have both sizable local markets and large, non-circuitous catchment areas served via those hubs. Airport congestion, customs, etc. are all problematic at NYC.
United (at EWR) and ANA (at JFK) have NYC local traffic well covered. East coast flow traffic is well served via IAD or ORD, which is why EWR-NRT is likely to have a very limited shelf life. UA will probably fly it for summer 2020, but it will quietly disappear in winter 2020-21. They are very unlikely to be called on it as a route case default.
Japan's polulation is in decline, and its economy has been stagnant for years. There is zero justification for additive service as a result of HND opening. This is just shifting service from one airport to the other - though it will be a major improvement for Tokyo travelers.