A bunch of them were complaining that Uber is being bad, requiring camera permissions, etc. The newer androids have nicer permissions systems, requested at runtime. But they are running Android 5* because the shiny turd of a phone they got supports only that, but looks awesome. AOSP is good and all, but I'll never buy anything that is not a Google device unless I magically have free time to root it and run an OS I trust (which might or might not exist).
The devices that google had and weren't using Qualcomm CPU got updates for a lot longer (e.g Nexus Player).
It gets very, very annoying for Google to try to support phones that use CPUs that don't update or release anything anymore.
Apple uses some third party chips but they haven't had that problem. Currently, iOS 10.3 supports the iPhone 5 - released in 2012. I suspect that iOS 11 when it comes out in September will keep support for all 64 bit iPhones. That would mean the iPhone 5s introduced in 2013 will be supported until September 2018.