As I already explained, those more extreme individuals plan these actions in more covert locations - smaller forums, subreddits, image boards, discord, telegram groups, etc. There are no rules banning such behaviour in these places. The owner and mods of KF actively not only delete such content but repeatedly remind people of the prohibition. They also actively report users who violate US law and fully cooperated with any legal demands brought by State and Federal law enforcement. Josh has even banned mods who disagreed or facilitated such behaviour outside the forums.
So kf is a target finding service. The nasty work is done "elsewhere", just like a good terrorists organization - keep the wetwork in small cells while the political arm directs them in plausibly deniable ways.