Adding code to the kernel to support new hardware is relatively easy.
Removing code that is no longer useful can be harder, mostly because it can
be difficult to know when something is truly no longer needed. Arnd
Bergman, who removed support for eight
architectures from the kernel in 2018, knows well just how hard this
can be. At the 2020 Linux
Plumbers Conference, he led two sessions dedicated to the topic of
obsolete software and hardware. With a bit of effort, he said, it should
be possible to have a better idea of when something can be removed.

Source: LWN.net – [$] Software and hardware obsolescence in the kernel