OP missed the point. I believe the reason devs keep the exploit on latest version is so that they can work with those to explore more about the console. The holy grail should be fully compromise a console's security. Let's say there is one kernel exploit found, and pre maturely leaked; Sony patches it, then the devs will need more effort to find kernel exploit on newer version to continue their research. For Sony is able to find the exploit themselves, it may take time and that give some breathing space for the homebrew scene to do the research. Giving Sony more advantage then in the big picture, only slow down the progress to achieve the holy grail.