The affected APIs were from packages where is is easy to tell from the name that they were not part of the standard.

These can be very useful in certain circumstances, but it should have always been clear that there is a risk they could one day be changed in an incompatible way or removed.

Does not change the fact that existing code, or existing JARs could not run any longer, and had to be rewriten.

When code breaks, the user doesn't care about the details of the root cause, it stays broken.

That code was never compatible with standard Java to begin with, therefore nobody should have been surprised. It would have never run on a JVM that didn't bother to implement the same internal APIs.

Crucially, if the OpenJDK project had removed or changed these internal APIs the result would have been all the same. But it's simply unreasonable to expect Oracle to also maintain backwards compatibility there.