Why do smartphones and SoCs require a custom build per model unlike PCs?

Question

Take Linux distros for x86: there's a single .iso for all devices Linux supports at all, be that laptops, desktops, servers, etc. And my 10y.o. PC is still getting updates smoothly.But then if we look at say Armbian, that seems to offer a custom image for every board supported, and those images are sometimes outdated for that specific model.Same for Android, there isn't just a single Lineageos image, every device needs its own, and all devices are always outdated because vendors forget about them in 2 years at most. Question is, why is it the vendor (or custom LoS maintainer) that determines when and if my Android phone will be updated, but it's not up to say Asus if my laptop is going to get an update?With Android I'd almost think it's done intentionally as part of planned obsolescence, but then why is it so with SoCs too and not so with x86?

pwg · Accepted Answer

> Why do smartphones and SoCs require a custom build per model unlike PCs?
Because there is no standard to which the SoC's adhere in the smartphone market.
PC's all adhere to the "IBM PC" standard (well, as extended along the way) so they are all similar hardware.
There is no such similarity in the ARM SoC smartphone market. Every variant of the SoC is different, such that different support is needed.
Now, as to why, that is a different question, and one to which any answer is just a guess. Most likely generic guess is because there was no need to be compatible with a standard from the beginning, and now they are all 'custom' in their own divergent ways.