Some of this is actually a surprise - we don't have a good handle on how influenza seasonality works, and some of the "Just So" stories for it should have promo

Some of this is actually a surprise - we don't have a good handle on how influenza seasonality works, and some of the "Just So" stories for it should have promoted influenza transmission, like increased indoor crowding above even the usual levels in the winter. The dynamics of influenza could have been expected to change, and I would have put money on they decreasing, but it is never the less not pre-ordained nor attributable to an obvious cause (for example, one of the original reasons people didn't push mask orders is the limited suggestion that they were effective for flu).