The only good explanation is Doylist, and it’s that Rowling hypercorrects for criticism of her works in the next book, which leads to a one-book delay.

People ask why Harry never helps Ron with money after the “Ron is poor” plot in Chamber of Secrets, then Harry gives his Triwizard winnings to Fred and George in Goblet of Fire.

People start talking about how Time Travel solves all plots after Prisoner of Azkaban, then the whole supply gets destroyed in Order of the Phoenix.