From an interview with Gary Sick, a national security advisor to President Jimmy Carter and an expert on the Middle East. Unlike most analyses of the verbal war between Israel and Iran, his makes sense:

As I said in my talk, when Israel keeps talking practically every day of attacking Iran, to me, that is the best evidence that they are not going to do it. If you look back at almost all the raids and operations they have carried out whether it was in Entebbe, in the alleged Syrian nuclear site recently, or on Iraq’s nuclear facilities in 1982, all of those took place absolutely without any previous warning. They were treated as state secrets. Israel knew that one of their strengths was the element of surprise.

In this case, by talking about it for several years, Iran has responded by diversifying its program; they have tucked away their supplies. The storage site that was recently found near Qom was clearly meant as an alternative option in case Israel bombed Iran’s main centrifuge site in Natanz. Iran has been able to put things underground, which makes it harder for a possible strike. It would be very difficult for Israel to destroy Iran’s program in a single strike. And they do not have the capacity to come back and bomb for several days or a month, the way the US did in Iraq.

Israel could do some damage but they could not wipe out the whole system. When they hit the facilities in Iraq, there was no defense, everything was above ground. There were no preparations made and it was a very straightforward bombing of a single target. That is not true in Iran today. It is a peculiar strategy to use because you are basically telling your opponent to take as many precautions as possible, or to hide the materials in question, and that is exactly what Iran has done and is doing. Israel can only hit specific targets on one occasion but cannot continue for several days. Iran will retaliate and things will be far worse.