History, inertia, lack of any demonstrated interest or unified direction, key Java players running away, a change in planned features every month, no clear incentive, almost no interest from Java programmers? (What interest there is seems to be mainly from the fringe community involved in Scala and Clojure, who want invokeDynamic.)
Wanna bet those are never going to make it in Java7?
Oh wait ... probably some half-baked form of those will ... after all, they are calling anonymous method blocks that DON'T capture the whole current context "closures".
Not to mention that they could've inferred the type of the requested function ... an instance where those half-baked generics could've actually been somewhat useful, instead of just a way to avoid explicit type-casts.
The whole language is fucked-up. They should've just froze it at version 1.4 and be done with it.