It appears my originally stated reason for why the attack was called off is legit
There are rumors going around that Iran got tipped off to the attack and did indeed have the American planes perfectly targeted. They knew that if the planes actually entered Iran, they would be lost. There are several variants of this story and I am waiting for which variant ends up being confirmed. The bottom line is that the attack was called off because Iran was aware of it and too many American assets would be lost. Trump's lines about "loss of life" being the reason for calling it off may not be reality and though I am sure he was concerned about it the people really calling the shots were not.

The U.S. was locating Iranian submarines when the drone was shot down
The Navy was operating a P-8 Poseidon anti-submarine aircraft alongside the drone. With the course it was flying, it was obviously attempting to locate Iran's submarines. It did cross into Iranian airspace, as proven by the fact that Iran got the debris and not the Navy, which went after it immediately. Iran beat them to it and the Navy could do nothing to prevent the Iranians to from picking up the pieces, a reality of it landing on Iranian turf. Iran shot down the drone to force the anti-submarine aircraft to leave their airspace without killing any Americans. This beyond proves that Iran not only can target American stealth, they can target it selectively and not hit a nearby aircraft. That's BAD NEWS for the U.S.

What is even WORSE news is that Iran did it at 4 AM, which means night attacks won't be beneficial against Iran.

CORRECTION TO PREVIOUS POSTS:
The drone shot down was an MQ-4C, which is basically a more advanced clone of the Global Hawk. A better score for Iran than a Global Hawk. ADDITIONALLY IMPORTANT: Iran was the one that recovered the debris, the U.S. navy did not, which means Iran was telling the truth about where it was flying to begin with. If they got it, it fell on their turf. It is really blown to smithereens, a direct hit. That's good for Iran because it proves their missile systems can do it, but it is bad because they don't have any big pieces. Additionally, there was an American P-8 spyplane accompanying the drone, Iran was able to differentiate between the two, and hit the drone. The P-8 was a much easier target. Iran obviously opted not to hit it because killing it's crew would have meant war.

It appears America is attempting to attack Iran's power grid...

http://82.221.129.208/.wi0.html