Because that’s what some of them in Algeria have got, allegedly.
Of course, since the plague can kill people, the unfortunate possibility remains that this may be used as a weapon. Deliberately infecting a large city would be devastating and have far reaching effects, as unlike crashing an airplane into a building, the plague can spread. A quarantine is necessary, and having a media blackout where this happened, while it might avoid panic, makes it harder to track down people who may have been exposed.
Al-Qaeda is apparently worried that it might spreading to Afghanistan. If it actually has reached there, it will devastate the population as the Taliban could easily have been exposed and accidentally expose other. That includes foreign troops fighting there. An outbreak there, while it might end the war there, would be devastating to the population, as even with treatment, the plague will still kill one in twenty victims. It would likely impact the poor the worst, and someone would undoubtedly blame foreign troops for the plague. It may not even be possible to treat every one, so let’s hope there is not a major outbreak.
And if this is due to bioterrorism gone wrong, it is horrifying.