As a point of comparison, Microsoft ships its OS across a variety of manufacturers and largely keeps it maintained across them (give or take some exceptions like enterprise environments & the like).
Even unlocked Android phones purchased independently of carriers have inconsistent lengths of support, so it doesn’t seem to be entirely a result of carriers, so…What happened here?
At this moment, only 1, Fairphone. (I’m looking into it now)
That is good to know, a big point to them. Unfortunately from what I understand they are a good concept, but poorly executed, as I have really only heard bad stuff about the user experience.