Some of the problems that made them finally quit from the JCP already existed with Sun. Anyway, I think Oracle made it worse, and I think Oracle is bad for the Java ecosystem. Oracle themself criticised the JCK licensing policy of Sun, but now, after they bought them, they did not change them. They even stated that they would develope Java however they want, even if the JCP votes against it.
This is another bad day for Java. But kudos to Apache and the others who have quit the JCP - I think that was the right move!