Because their console is doing bad and PS4 is a sales champion.

Despite calls of the console being doomed in Japan being premature, PlayStation 4 is doing terrible numbers in Japan at the moment:

As poorly as the 3DS, Vita, and Wii U sold in their first 13 weeks, the PS4 is selling even worse. And as everyone has said, it's because the system is hugely lacking in games that appeal to Japanese audiences. But I don't think it's as simple as saying "Just wait until Kingdom Hearts and Final Fantasy XV!", as those are two games with no release dates coming from a company infamous for its long development times.

For now, and for the forseeable future, the PS4 is not going to sell well... because the titles releasing this year are not the ones that sell systems. A bunch of Western games and niche Japanese titles are not going to reverse the trend of the PS4 selling poorly in that reigon. Sony was/is so focused on grabbing the Western markets that it's either forgotten or ignored the eastern one. 2014 is going to be rough on the PS4 as far as Japanese sales go, and there's not much being done to turn that around.

You make a good point, but the Vita also had a pretty poor start (not quite as bad, but still relatively terrible), and now it's been picking up steam since developers are jumping on.

Japansese developers tend to stick with older consoles for the first year as a transition period, and then they start developing legitimately for newer consoles. 

Although, like you said, if major games like Final Fantasy XV and Kingdom Hearts III take too long it will be a lot harder to recover, but if the rumors are true and Final Fantasy XV comes out either this year or next, I think the PS4 could do just as well as the PS3 did.

I don't think Final Fantasy XV will come out that early at all.

But there's Metal Gear Solid V still.

not in Japan

In Japan, like everywhere else, one of them has a future while the other has played all it's cards.

really? So there is no games in the future for Wii U? Nintendo is doomed!