All the Android manufacturers, with the exception of Samsung, rely on their parties for hardware components and therefore device driver binaries that would need supporting and patching. And all of them including Samsung rely on Google for OS patches (well, except Google). Third party firmware is why Google struggles to support their devices for more than 3 or 4 years.
A lot of manufacturers wouldn't even exist after 10 years. Blackberry, Nokia, Palm, all gone in the last 10 years. HTC were big back in 2011 but gave up on phones a few years ago. I'm sure there are more I'm forgetting.