Because that is the nature of these SBCs. They aren't some generic queryable platform running UEFI. Instead you have a bespoke OS fork for each individual board

Because that is the nature of these SBCs. They aren't some generic queryable platform running UEFI. Instead you have a bespoke OS fork for each individual board. This means that vendors need to give a lot of attention to the software because there isn't a foundation or company taking care of all SBCs at once. The device becomes obsolete very quickly if you can't install recent software. SBC performance hasn't increased much. There are still plenty of boards with A53 cores that have been used for more than a decade.