This is a really difficult question as we do not know for sure why some areas remain politically unstable. We can, however, speculate. We can say that some of the Middle East’s problems are common to other politically unstable areas. Others, meanwhile, are specific to the Middle East.
The major factor that is common to many areas is the fact of having been colonized. Many areas of the Middle East were under foreign domination for a long time. This caused, for example, countries like Iraq to be set up in somewhat unnatural ways. That is, they encompassed different ethnic and religious groups within the same country. This makes for unrest. Also, countries that were colonized often did not have native people being taught and prepared to govern themselves. This meant that, when these countries became independent, they did not have people who were ready to step in and govern modern countries. Finally, this area had no history of democracy. Therefore, its people generally did not even try to set up democracies, leading to conflict because much of the citizenry is without a voice in politics.
In addition, there are reasons specific to the Middle East. The most important of these is oil. Much of the Middle East, of course, has vast oil wealth. This makes control of the governments very lucrative and it makes people want to wrest control from those who have it. The second, and related, factor is that the rest of the world is very interested in the Middle East. The oil in the Middle East means that countries have vied for control of the area and have helped to stir up trouble in the region. This was particularly true during the Cold War. The outside world was also instrumental in creating the state of Israel, an action which has also contributed mightily to the unrest in this area.
In other words, there are many reasons why the Middle East is so turbulent.