Oracle's in it for the money
As I understand it, the only way Sun (and now Oracle) makes any money off of Java is buy licensing it.
Everything is open, except the test kits (TCK's) that you need to get your version of Java certified. Those you have to pay Oracle for. That means you can create your own java implementation without paying Oracle. And Oracle is suing to say that you can't create your own java implementation and call it something else.
If the TCK's were open source, and Harmony went forward, how would Oracle be able to make money off of Java? Harmony would be a fully open end run. Everybody that is paying wants this. Everybody that is getting paid (Sun, then Oracle) don't want this.
When Oracle didn't own Java, they felt differently. After they spent a ton of dough to buy Java, they are trying to continue making money from Java. And why wouldn't they?