It's an exceptionally odd decision, but planned for approx. a year now.

- First they stopped allowing download of purchased books for cable-transfer to kindle in 2025.

- Then they amped up their effort to avoid jailbreaking by suddenly releasing more firmware updates than before.

- Now they stopped supporting a wide range of kindles.

Amazon obviously assumes that they sufficiently killed the competition so they don't need to worry about customers leaving.

As for me, I managed to exit on-time, applied a jailbreak on my kindle touch and now buy my books elsewhere...