Their technical reasoning is falling apart and they are taking a huge project with an inexperienced team. I don't think it's NIH syndrome, everything is pointing to copyright.
They want complete ownership of the copyright for the DS.
Maybe to have leverage with HW vendors or dealing with proprietary sw.
Ubuntu-For-Android project, I think that when this transition takes place, Ubuntu will be the only vendor with an offering that's sensible, and consistent.
It's a big if, but if it does happen, they'll make everyone else look clunky.
Google might still surprise here too, but I've used ChromeOS and it's hugely underwhelming.
The first company to have a seamless transition from phone sized form factor to tablets and monitors will be the next king for a while. Windows 8 is _not_ it. And I do expect that this is their primary motivator. If not, then I can't even begin to guess what the hell they're thinking.
But the past year or so hasn't looked so great as it seems they're losing focus on that desktop experience. Granted some of this stuff got foisted on them from the GNOME-skulls which kind of forced their hands in some ways, but overall it seems quality is dramatically decreasing and many decisions are baffling.
At this point it isn't too far off from all the other awful distros out there.
Actually, this entire thing is happening just to generate more ad revenue at phoronix. Nice work, Canonical!