In Iraq is was different. Thousands of Iraqis obtained bomb making skills, often from Russian instructors, during the 1980s war with Iran. In that conflict, roadside bombs and booby traps were a favorite weapon against the aggressive Iranians. After Iraq's invasion of Iran in 1980, the Iranians soon recovered, and were on the offensive for the next seven years. The Iraqis had a hard time stopping the enraged Iranians, who eventually agreed to a ceasefire in 1988. The thousands of Iranians lost to the Iraqi roadside bombs and booby traps played a role in the decision to stop the war. The Iraqi veterans who built those bombs were disproportionately Sunni Arabs. Saddam did not want Kurds or Shia Arabs knowing how to build these battlefield weapons that could also be used by terrorists.
Those bomb making skills went unused through the 1990s, but in 2003, there was again demand. And the demand grew as Baath Party and al Qaeda money was spent to try and regain Sunni Arab control of Iraq. That hasn't worked, but the bombs have killed nearly 800 Americans, and many more Iraqis.
Iran noted the Iraqi use of improvised bombs during the 1980s, and established their own bomb making schools. There, Hizbollah bomb makers from Lebanon were trained to build bombs, for be use against Israeli troops. In the last few years, some of that bomb making knowledge has been shared with Palestinian terrorist groups like Hamas, and Shia Arab Islamic terrorists in southern Iraq. Iran is believed to have also trained some al Qaeda terrorists, although that is hard to believe. Al Qaeda has a policy of killing Shia militants at every opportunity. But because of the pressure from Western counter-terrorism efforts, al Qaeda and Iranian terrorists appear to have engaged in some cooperation. This may have included sharing bomb building knowledge.
Islamic terrorists who know how to build bombs have become a major target for counter-terror operations. The bomb builders are relatively rare. Far more people are willing to plant the bomb, or set it off. As the Israelis learned in the last five years, if you want to stop terrorist bombers, concentrate on the bomb builders. The Palestinians didn't have too many to begin with, and they were often highly educated, or simply bright, individuals who applied their skills to the dangerous task of building bombs.