Because the plane is nowhere near Japan? But of course, your remarks are not surprising in the least, coming from where you are.
They should send its entire navy to the East China Sea to look for this plane. Even if it takes years, and nothing turns up, they should continue searching for it there.
Furthermore, they should substantially increase the size of their navy to intensify their search as much as possible.
They should send their entire navy to the East China Sea to look for this plane. Even if it takes years, and nothing turns up, they should continue searching for it there.
They could use the Senkaku Islands as their base of operations in conducting the search.
In other words, be careful what you wish for.
But in all seriousness, the plane disappeared far from Japan, it wasn't travelling to or from Japan, there's no evidence that it ever approached or entered Japanese Airspace or appeared on Japanese radar, and there were no Japanese nationals on board.
