Al Qaeda has long realized that religious fanaticism is not enough. It’s no longer enough to proclaim that God demands suicidal attacks on the enemies of Islam. There are fewer Moslems willing to die, or even risk their lives, without some kind of earthly reward. Now some Islamic terrorists are being more public about the long-popular system of cash rewards for killing the enemies of Islam (or at least al Qaeda or whatever other Islamic radical organization involved).
This is not new. For decades cash payments have been made to terrorists (or their surviving families) for accomplishing specific goals. In part, this was necessary so that the terrorists could feed and house themselves and their families. For particularly dangerous work even higher rewards were offered, as well as bonuses. In Iraq and Afghanistan bonuses were often paid for killing an American (or any foreign) soldier. Even larger rewards were paid for capturing a foreign soldier but this was rarely accomplished.
These payments, rewards, and bonuses were good for morale and recognized that terrorists were often in this dangerous business largely because they needed a job. Once that became common, cash rewards were a natural follow on.