In the context of Linux on embedded and mobile breaking user space would lead to hardware manufacturers essentially freezing on the kernel version right before the break. (For both new projects or in the exceedingly rare case where they upgrade deployed devices).

This would be exceedingly unwise and pushes against the vast amount of effort the kernel community is expending to secure the kernel and bring OEMs on non ancient versions of the kernel.

Essentially these are not old devices, they are new and you likely have purchased some of them without even knowing.