Because a potential problem may have been identified,it is just that...potential.It's a ghost and a tool of mass paranoia.It's what the terrorists want.
Myself,I'm going to wake up in the morning,breathe the fresh air and go about my business as I always have.
There's at least one good reason for them not to use it...
A highly contagious bioweapon would spread throughout the entire world quickly, given how much mobility there is in the modern world (people on airliners, etc.)
...including to the terrorists' homelands.
And even if they're too callous or stupid to care about that part, the fact would remain that *every* country which suffered a large death toll would undergo the kind of epiphany that the US did on 9/11 -- and come to the inescapable conclusion that terrorists are too recklessly dangerous to allow to exist.
Contagious bioweapons are like a nuclear weapon that, when you trigger it, goes off all over the world, in uncontrollable random locations.
Anyone with half a brain (and for all their faults, al Qaeda isn't *that* stupid) would realize that contagious bioweapons would be a more certain death for the user than for the intended target.
Pissing off *everyone* is counterproductive to *any* cause.