Oracle is, above everything else, about monetization. If they can't make money out of it, they will either change it so they can make money out of it, or they'll kill it.
Sun was generally good at open-source (though not perfect by a long shot, OpenSolaris was not exactly a slam dunk and the CDDL was rather weird — and explicitly and expressedly made incompatible with the GPL), but they were rather bad at monetizing. Oracle's the exact opposite.
It also realizes that most of its monetization comes from professional services, and saw that 1) software subscription revenues were declining across the board, proprietary or Open Source, and 2) Open Source created (to IBM's lawyer's eyes) a possible threat to its patent holdings (a considerable revenue stream / business value themselves) which was best addressed by keeping core development outside the organization (Red Hat, Novell/Suse, Kernel.org, Apache.org).
Oracle's direction (as was Sun's somewhat schizoid approach to Free Software / Open Source before as noted by its supporting the Caldera/SCO Group attacks against Linux) are making it a non-credible source. Hence the forking of projects (Lumina, LibreOffice, OpenJDK, MariaDB, etc.) it had inherited.
Q: Why hasn't Oracle ruined Virtualbox yet?
A: Because they're going in alphabetical order.
But really I think the only thing saving Netbeans' butt is Java.