Not just licencing issues
No doubt "licencing issues" will be cited as the reason why the transition of Java to Open Source is taking its while.
I strongly suspect that this is not the whole story.
Having attempted to work with the OpenOffice.org source code {which originated as the closed source StarOffice} and seen what thoroughly awful techniques people thought they could get away with because they never thought anybody was ever going to see the source code, I can say it's more probably because Java is riddled with embarrassing bits that Sun want to get rid of before letting anyone else see the code!