Always looks better if you lower expectation then exceed them in the end, looks better for investors (though it's not how it really works I reckon).
They recently got a white PS4 Slim and there's DQXI coming out soon which should push it a lot.
But yeah it's rather strange that expected to ship/sell less this year when it's already well ahead of last year so 22-24m incoming?
Last year had the PS4Pro launch, Y5,00 price drop in Japan in September and FFXV.
Outside of DQXI there is not really any game on the PS4 that's expected to sell over 500K from August till December in Japan. PS4 has had a steller lineup thus far this year much better than the first 6 months of 2016. Still PS4 could very well do a little better in 2017 in Japan compared to 2016 but it would only be between 100-300K more so it's not as substantial. In the end Japan is just another market for Sony and it's not really key in terms of yearly hardware targets.