This might sound outlandish but I think it's because Apple Park is finally finished and they have moved in. Think about it. The five years that building was under construction has been torture for Apple fans. Few updates to desktops/laptops. Long waits for iPhone orders. Last update to the iPod touch? Back in 2015 and they don't even mention the lineup at events anymore.
I know they have tonnes of engineers and software folks but for a while now I've suspected that Apple had bitten off more than it could reasonably chew. There has a been a considerable slowdown even to just processor bumps in desktop/laptop hardware (hey there Mac mini). Now that the new campus is settled perhaps we'll start to see more hardware updates more frequently. We keep talking about availability for this years order so consider that last year the talk was about constraints because of difficulty mass producing the FaceID hardware. This year they are making enough for the Xs, Xs Max and however many for the five colors of the Xr and enough A12 Bionics for each of those as well.
Just my ¢2 but this year might mark the return of the Apple that Steve Jobs spoiled us on for the five glorious years prior to his passing.