They haven't. It's simply this issue.
I have repeatedly asked people in many religious circles this question that we have so many of these ulema and mashaikh talking a big game about Jihad, etc. And yet why don't these "elders" just get up and start a military movement themselves? Why don't they just ignore the common people, the common people aren't gonna listen to them anyways, and instead go on a Jihadi mission by themselves, only these "pious" ulema and mashaikh? No one can satisfactorily answer this question because the truth is too horrible to think about.
Despite all that is being said and done, no one is ready for that kind of a mission. Ready spiritually, I mean. The level of iman and tawakkal needed for Jihad is not child's play. This is why I scoff at the idea of Mahdi appearing in these times. We don't even have 13 people who could seriously pledge their lives to Jihad right now, forget the 313.