What is spite?
"Why is it spite to retain an important property, one that you not only paid for..."
I'm not sure you know what "spite" is. In fact, you ask this as a rhetorical question, demonstrating as much.
You imply that spite has to have a "reason". It's not revenge! It's not rational. This won't be some sort of justified reaction. They'll do it because they can. They have power and can do it.
They're doing it for spite because they are a spiteful, hateful company, as demonstrated through their business practices for as long as they have been in business.
It's also a figure of speech. People often say "doing it out of spite" when what they really mean (in this case) is "doing it for spite". Not because they are experiencing spite, but to cause it. They'll do it deliberately to make everybody mad, for lulz. Oracle has demonstrated, repeatedly, that they are that kind of company.
Hmm, Oracle hasn't really been cranking the "goodwill handle" for the last few decades, has it?