The problem is really that the SoCs aren't maintained for long, and the complexity of the SoC concept makes maintaining it yourself as the device manufacturer a

The problem is really that the SoCs aren't maintained for long, and the complexity of the SoC concept makes maintaining it yourself as the device manufacturer at best impractical, maybe even impossible if the SoC manufacturer won't release necessary source code to you. They want it this way because then they can sell more SoCs because users end up upgrading more often, and device manufacturers (besides Fairphone) don't complain because their interests are aligned. On the Apple side you see devices getting support for much longer as Apple designs and maintains it's SoCs in-house, and at least to a degree value device longevity because that keeps second-hand prices relatively high, and that aligns somewhat with Apples interests. Not quite 10 years, but we've seen feature updates for just under 7 years with the iPhone 6s (released 2015), and it's still receiving security updates and bug fixes.