Why Have No Terrorist Groups Been Able to Execute a WMD

Why have no terrorist groups been able to execute a WMD attack with massive casualties?

A) Most groups lack the motivation - the acquisition is always a very hard to overcome obstacle.
B) In reality, most WMD agents are not naturally weaponized and figuring out how to do so is extremely complicated.
C) Affecting a wide variety of people is difficult, especially in a way that the attacker can get away.
D) Having the WMD perfect storm of all three components is difficult.