because there isnt an Iranian plane with a Chinaman's chance in hades of getting through Iraqi airspace (currently patrolled by the US) or Israeli airspace on their eastern front to drop a bomb on anything significant, thats how....
Are you familiar with the concept of a medium range missile? And the news isn't so hot on missle defense testing the past six months.
The Iranians if they chose would probably go through Saudi/Jordanian airspace for a retalitory attack. They have the means to do so with both F-4s and Su-24s capable of long-range missions. Their airborne tankers are still noted active and the Su-24 can be buddy-buddy refuelled. They have this option, but it would be a suicidal one!