As much as Islamic terrorists preach the need to make attacks in the West, they have been remarkably unsuccessful doing that. In the last decade they have managed three attacks (September 11, 2001, March 11, 2004 and July 21, 2005). They were more successful in the 1990s (February 26, 1993, June 18, 1994, July 25, 1995, December 3rd, 1996, and February 23, 1997). There were also many more attacks on Westerners outside Western countries.
However, the September 11, 2001 attacks changed everything, and led to a determined response from the West (the "war on terror"). Many Islamic terrorist leaders believed that this response would enrage the Moslem world and cause even more attacks in the West. But it didn't work out that way.
Two things happened after 2001 to disrupt the terrorist strategy. First, there was the 2003 invasion of Iraq, which forced Islamic terrorists to fight on their own ground. This led to Moslems fighting Moslems, as other Moslems had always been the most numerous victims of the terrorist attacks. The main reason for turning their attention to the West was the inability to make much progress against the rulers of Moslem states. The Islamic terrorists considered these leaders corrupt and tyrannical. They were correct in that assessment, but these despots were also very good at suppressing any dissent, and Islamic radical organizations had suffered several major defeats in the 1990s (mainly Algeria and Egypt). The West was considered more vulnerable, and operations in the 1990s seemed to confirm this.
But Western counter-terror specialists had an ally that had developed an effective strategy for disrupting Islamic terror attacks. Israel, under attack by Palestinian terrorists since 2000, had found a vulnerability. Islamic terrorists who know how to build bombs are relatively rare, as are several other kinds of specialists. Far more people are willing to plant the bomb, or set them off, tasks which require little skill. The Israelis quickly figured out that, if you want to stop terrorist bombers, concentrate on the bomb builders and other skilled people. The Palestinians didn't have too many of these specialists to begin with, and they were often highly educated, or simply bright, individuals who applied their skills to the dangerous task of building bombs and getting them to targets.
So the United States concentrated on tracking down and capturing or killing the bomb makers. This began in Afghanistan, where dozens of training facilities were shut down. It was believed that all the bomb building knowledge on the Internet would take up the slack. That didn't work. The Islamic terror groups tended to attract a disproportionate number of uneducated, and technically inept, recruits. These guys had a hard time following instructions, as the growing number of bombs not going off, or exploding while being assembled, has demonstrated.
Bomb maker shortages are now quite acute anywhere that Islamic terrorists are active. This has been acknowledged by Islamic terrorist leaders, who now simply call for all their followers, especially those in the West, to just do whatever they could to kill Westerners, preferably in a manner that will make the network news. The drought of attacks in the West, and the growing number of Moslem victims in the Islamic world was killing the Islamic terror groups in the popularity department. Not in the West, but among the people they purported to represent.
All this is a bit ironic, as the Islamic terrorists are not only against corrupt and irresponsible rulers in the Islamic world, but they are also hostile to Western education, particularly the study of modern technology. The Islamic world is already in the basement when it comes to literacy and technical education. That alone causes a shortage of bomb makers, or those who could acquire the skills. Now the terrorist organizations are to diminish the number of educated Moslems even further.