I've run into this a few times with Apple. It's not that the upgrade is explicitly not allowed by policy. It's just that things are broken in ways which prevent you upgrading/using the device properly. I don't know if it's just lack of care on Apple's part, incompetence, honest mistakes or a stealth method of forcing an upgrade. In any case, hardware that seemed slow and outdated with Apple's software ecosystem now runs perfectly with Ubuntu. ¯\_(ツ)_/¯
I suspect it's more that maintaining a 10+ year testing matrix across three architectures and like 15 product families is pretty un-manageable.
The cross product matrix is already staggering, but imagine testing 10 years of iPhones, 10 years of iPods, however many years of Watch, AirPods, chargers, etc against every Mac released for 10 years - in every configuration? Every time you ship an OS update? Wild.
I've had a similar experience, where supported OS updates rendered a macbook effectively unusable due to performance hits and bugs.
It's one of several reasons that I stopped buying macs for my personal dev machine and switched to ubuntu. Linux certainly isn't perfect but updates have been more pleasant than on mac or windows.
