IIRC HND was historically slot restricted and mere months before COVID happened there were an additional 50 slots granted due to relaxed rules about over-city flying. I think the upcoming olympics probably had something to do with this as they needed to increase capacity.

So there was an addition of HND services as well as migration of flights there from NRT when appropriate since HND is more convenient in several ways as you said. For example ANA added an SFO-HND service and planned to move their SJC-NRT service to HND.

COVID then hit and so a lot of these plans didn't happen, and when cuts occurred it was often better to keep NRT routes as NRT tends to be better for connectivity to elsewhere in Asia which was the most important thing when very few on the flights to Japan were O/D traffic.

So what we're seeing is probably just the resumption of plans that were put on hold by COVID, now feasible with Japan's reopening, etc.