If you start distributing a jailbreak, Apple will patch it. If you sell it to an organization that buys exploits, you can enjoy your exploit indefinitely and make a nice chunk of change on top of it. Apple benefits from this dynamic greatly, as their App Store revenue is more important to them than their uses' security. They incentivize hoarding potential jailbreak exploits and selling them to the highest, and most likely malicious and deadly, bidders, instead of sharing them with users to increase their freedoms.