I think it's fair to say that JL doesn't see connecting pax from US - SIN (KUL too, I guess) as a core part of their business. Those flights ex-NRT are not timed for making the connection from AA/JL flights from the US, nor are they timed for most connections from Europe either.

I do find it curious that they decided to cut the evening flight rather than the daytime one. The evening NRT-SIN flight allowed for a nearly full day in Tokyo and only ate up the evening. Though most need a full day in Tokyo are probably closer to the city center, and the ex-HND flight serves them better.

Airlines tend to make more money on O&D traffic than connecting. I wouldn't be surprised if the flights retained had higher O&D traffic, and I'm guessing that's part of the strategy.

Does anyone know if the aircraft on this route alternate NRT-SIN-HND and vice versa? The timing suggests that. Keeping the a/c otherwise on the ground overnight or all day in SIN doesn't seem efficient.

All of this isn't exactly good for AA flyers, who are so heavily reliant on JL to connect onwards to Asia. Other threads exist on how getting AA codeshares on JL is getting much harder. The other two big airlines can fly onwards on their own metal. Then again, these schedule cuts are preferable to having a defunct partner for onward travel, so if this strategy ends up keeping JL afloat, it will likely be worth it.