The U.S.'s opposition to Iran is almost purely based on the Israel Lobby.The Iranian Revolution happened in 1979. The late Bush era corresponds to the late 2000's. There's nearly thirty years in between.
Not least because of Iran making sure American occupation forces will have a rather hard time in those countries.
Besides the fact that, as pointed out above, at least some three decades passed between the Islamic Revolution that saw Iran engage in an principled anti-imperialist policy and the USA's strategic shift towards containing China, all this means is that Washington does not have a military option against Iran. The USA regime always has other concerns in addition to Iran, so that isn't really a valid contention.
The Israel Lobby doesn't dictate the U.S.'s foreign policy continuously.
Iran never posed much of a threat to the U.S. at any point in time.
Consequently, the U.S. generally had Iran as a low priority target.
Basically, Iran was always a "target of opportunity," which was to be tackled when not focusing on more important things.
You are somehow forgetting that the U.S. was fighting the Cold War with the USSR until ~1991, and then was fighting to annex all of the Soviet Sphere of Influence after the Fall of the USSR.
The U.S. didn't completely finish rolling up the Soviet Sphere of Influence before China appeared on the Radar.
This is why Syria was left unfinished.