This has nothing to do with people not WANTING to share, they are keeping it back for some very good reasons.
The longer this exploit stays private, the longer they might have to explore the wii u firmware even on newest updates and continously drive the scene forward.
Imagine if they suddenly decided later today to release it. Then what?
Nintendo would immediately patch it and that was it.
Eventually it might be fixed without them releasing anything to the public, but by then they might have achieved quite a lot.
An exploit/a vulnerability by itself is nice, but not very useful.
The hackers and developers are the people who actually make it worthwhile, so grab a lollipop and be patient.