The hardware could be completely capable of handling it but the software isn't. A lot of times when you buy an ARM SoC it comes with a supported kernel from th

The hardware could be completely capable of handling it but the software isn't. A lot of times when you buy an ARM SoC it comes with a supported kernel from the manufacturer and some documentation(but sometimes for various reasons a lot is missing). To ensure that you can always port the newest version of Android to a phone you need to ensure you can port the newest kernel. Limiting yourself only to well supported mainlined chips or to chips that you have all the documentation you need to maintain your own branch greatly limits your options and can run up costs a ton.