It's not rocket science. Rightly or wrongly Canonical has decided that the future of general computing is in the mobile space and they are working on getting Ubuntu there and bridging the gap between the mobile computing experience and the desktop computing experience.
In simplest of terms, they're trying to make a distro that can be both a phone and a desktop all in the same device. Again -- rightly or wrongly -- they have decided that they needed to move certain things in house to best accomplish that goal (Mir) and needed a specific interface they were in control of to scale between display form factors (Unity).
If you are a person that thinks this direction is wrong and will hurt Linux in the long run, then you belong in the "bad for Linux" category. I'm a person that thinks this is absolutely the best way for Linux to finally have its "year of the desktop" similar to how Apple made their comeback but with a twist -- by providing a compelling mobile experience with a device that just so happens to be able to double as someone's desktop when they want a bigger screen.
Pay attention to plunging desktop sales numbers. As people find ways to make mobile devices and tablets their only computing devices, this strategy will start to look smarter and smarter. Whatever else you think of Canonical (and by extension Ubuntu), this will either make them or break them.