The April 16, 2016 earthquake in the Kumamoto region wasn’t as severe as the 2011 Sendai quake, but it hit in a region where a number of semiconductor and electronics plants are located. In particular, a key Sony image sensor plant was damaged, and sensor production was stopped for a month and won’t resume fully until August 2016. Nikon uses a lot of sensors produced in that Sony plant, plus had other small suppliers in the region that were affected.
A number of Coolpix cameras got postponed to an October 2016 delivery, while DSLR sensor production was also impacted. Fortunately, Nikon had some supply of some of those DSLR sensors, so could continue to produce limited quantities of the affected cameras. For the most part the only camera not directly impacted was the low volume D5, whose sensor is produced elsewhere. A few cameras that have been in production for awhile (e.g. D7200, D610, D750, D810) tend to also have been less affected.
Rumors have it that products that were to be announced in the first half of 2016 by Nikon got postponed because of the quake, as well. In particular, the update for the D3300.