Lawyer-resistance; remember the situation a year or so ago when the tzinfo files were the subject of a patent claim? Oracle's weren't at risk because they have lawyers on retainer.
No, this is about write-once-run-anywhere compatibility as the other responses say.
(Incidentally, it was a copyright claim, not a patent claim, but in this regard they work the same way.)
Oracle's got enough cheddar to take it to court or settle out-of-court like their business depends on it.