Apple don't give people the tools/keys/etc to load new OS (etc) onto a device once it's no longer supported.

So, at best the device can just be used with the latest version of the software Apple allows until it's a security nightmare and better off no longer used.

Instead, if Apple gave people the ability to load something (prob a Linux) onto those old devices, then those old devices could be used usefully for quite a few more years.