This comes down to license and copyright e8hffff, thats all this is. With Wayland Canonical can't dictate its direction, with Mir they can-- more specifically thanks to the CLA they can even change the license of it at will. Now, I'm not saying CLA's are evil, I'm not Funkstar, but quite frankly...I dont trust Canonical anymore.
They've been making it very clear that they want to be the only name in the Linux ecosystem and want any projects they use to be under their control-- hence Unity, Mir, Ubuntu Software Center, hence the lack of even the word "Linux" on their website. They WANT to distance themselves as far away from the "Linux" Name as possible, because it implies community and NOT a single company idea and thats exact what Canonical wants-- a single company ecosystem.