It is speculated about shortages in Wii U CPU's production. Mitsumi Electric Co. Ltd. supplies pieces for Wii U hardware and it seems, they are having problems to deliver them.
It's not cost effective to maintain a chip line if you're not selling enough. Usually they ask for a huge premium or a last-time buy.
It's based on the PowerPC 750 which nobody is making anymore. Not in the ATCA format anyway... I've had to move some products to Freescale Book-E because of that. It's painful.