The silicon could go on for decades if both the modem and processor were fully documented hardware that the community can access and support in the Linux kernel.

I can run a secure and current form of Linux on 30+ year old hardware if I want to, because the hardware documentation was expected by everyone at the time even if some end users were oblivious to what this meant. The whole reason google pushes Android is because they provide a base Linux kernel that hardware manufacturers can easily slip their proprietary junk into without requiring them to add the kind of open source code needed for mainline kernel support by the community. This is the mechanism that depreciates your device. It is totally artificial and an end user exploitation by design.