Why has Iraq, and other Arab countries, tolerated a long string of dictators and tyrants? For the same reason many other countries, like China and Russia, have; it's the only form of government those nations could come up with that created some form or order. The price was a general loss of personal freedom, economic mismanagement, and wars with neighbors. Democracy is a far superior form of government, but it requires a lot more from the population. More personal responsibility, less corruption, and a greater willingness to work out compromises. Many Iraqis are not sure their country has enough of all that to get a functioning democracy off the ground. Should the new Iraqi democracy prove weak, a new strongman will surely appear. There are many waiting in the wings. For over a decade, Iraq's neighbors, and countries like the U.S., hoped to replace Saddam Hussein, not with a democracy, but with a "more reasonable" dictator.
In a pattern that is very common in the Middle East. A successful dictator takes control of the security forces (especially the intelligence agency and secret police), and then uses the national wealth to pay off enough people to keep himself, and his inner circle, in power. The majority of the population is kept in line via terror and poverty. This was how Saddam did it, and there are many Iraqis who know how this works and would not mind being a part of it. The part on top, of course.
What is radically different this time around in Iraq is that the Shia and Kurdish majority, for the first time, have the fire power to keep the usual source of dictators, the Sunni Arabs, from taking over. So the most likely elected president, or next dictator, will be a Shia Arab (which comprise 60 percent of the population.) At the moment, Shia leaders are not very respected. Many collaborated with Saddam (who bought off, drove into exile, or killed off, powerful business, tribal and commercial leaders.) Shia religious leaders are the most respected, especially those who stood up to Saddam (and usually had to flee the country, usually to Shia Iran).
It's something of a gamble, the upcoming elections. The people elected to the presidency and parliament could simply get together, decide to restore dictatorship (in the name of "order"), and that would be that. But there is a new idea circulating around the Arab world. Since the 1990s, many among the chattering classes have been suggesting that, perhaps all the woes of the Arabs (economic, political, diplomatic) are not the fault of others, but of the Arabs themselves. This is not a popular concept, but it has been getting louder, and more acceptable. Personal responsibility is not well received among Arabs, many of whom consider it "un-Islamic." After all, "Islam" means, literally, "submission." What happens is God's will, not, as the Infidels (non-Moslems) say, individuals acting as their consciences dictate.
So in Iraq, it's not just a matter of politics, but religion and culture as well. It's not a matter of who the next dictator of Iraq will be, but whether the Iraqis are willing, and able, to rid themselves of thousands of years of dictators to try democracy.