Militancy - Why do They Persist?

When United States military had managed to kill Osama bin Laden in 2011, the world had thought that the war against militancy would soon be over.  So did Sri Lankan government when they killed off Vellupillay Prabhakaran in 2009.  And so too those who had fought against Nazi Germany, when Adolf Hitler killed himself with his wife, Eva Braun in an underground bunker just before the fall of Berlin to Soviet Russian onslaught.  Thus, when United States announced that they had managed to kill Abu Bakr al-Baghdadi, the head of ISIS / IS / Daish, they had not actually accomplish any objective but merely pushing the organisation further underground.