> Why would that happen? please elaborate on that.

Because then it will just be a matter of drivers. Currently, as you say, they need to polish other things like camera handling, audio etc... But once this work is done, it's done. Then porting to new devices should be just a matter of drivers.

> I used to run ubuntu on the nexus 7 in 2013

Today they are bringing an usable touch interface which was not the case.