I think carriers want a platform that enables them to embed their own services. They'll have to weigh up the cost of a license for an OS against how much they could make from controlling their own 'ecosystem'.

Is Ubuntu Touch going to be completely open source? Jolla seem to be making a lot of noise about open source but it seems they're not really committed to it.

A fully open OS could gain a lot of favour with countries/individuals not too keen on being spied on by the USA. I guess some will have been duped by the mock outrage of Apple, Google and Microsoft into believing they were pawns rather than willing participants in the Prism scandal but they'll still be plenty of others who'll prefer a device with an OS that's open, transparent and not North American.