Then why haven't they?
Not very familiar with recent history are you? Oh, and as for your other rude comment, get over yourself.
I'd direct you to this link for further edification:
Here is an excerpt from that article re: Hezbollah's killing of Americans in case you're not a link clicker...
THE HEZBOLLAH MODEL
In the U.S. demonology of terrorism, Osama bin Laden and al Qaeda are relative newcomers. For most of the past two decades, Hezbollah has claimed pride of place as the top concern of U.S. counterterrorism officials. It was Hezbollah that pioneered the use of suicide bombing, and its record of attacks on the United States and its allies would make even bin Laden proud: the bombing of the U.S. marine barracks in Beirut in 1983 and the U.S. embassy there in 1983 and 1984; the hijacking of twa flight 847 and murder of U.S. Navy diver Robert Stethem in 1985; a series of lethal attacks on Israeli targets in Lebanon; the bombing of the Israeli embassy in Argentina in 1992 and of a Buenos Aires Jewish community center in 1994. More recently, Hezbollah operatives have plotted to blow up the Israeli embassy in Thailand, and a Lebanese member of Hezbollah was indicted for helping to design the truck bomb that flattened the Khobar Towers U.S. military base in Saudi Arabia in 1996. As CIA director George Tenet testified earlier this year, "Hezbollah, as an organization with capability and worldwide presence, is [al Qaeda's] equal, if not a far more capable organization. I actually think they're a notch above in many respects." Credit: Daniel Byman