I just don't think they care to, it's not how they fight. Their fighters are literally suicidal brainwashed volunteers who really do think that if they die fighting Americans, they're going to paradise, so why equip them with anything more than a secondhand AK, grenades, and/or a suicide vest?
Uh...
Not exactly up on the latest insurgent tactics, are we? Stand off weapons, mainly IED's, are the choice of Iraqi insurgents. True, foreign insurgents tend to be a bit more on the wacky brainwashed side. The locals are a bit more pragmatic.
I swear, every insurgent war that comes along, folks keep believing it'll be the Battle of Omdurman. For you non-history buffs, Khartoum, Sudan, 1885. The British were busy expanding their empire by killing plenty of the wogs. After the locals got honked off at being conquered, they slaughtered "Chinese" Gordan and a British detachment. The Brits sent a revenge mission 13 years later to deal with 'em. el Khalifa ordered 60,000 to attack hey-diddle-diddle-straight-up-the-middle. .... Against emplaced Maxim MG's, field guns, and long range arty. The results were predictable. The Mahdi Army lost 22k, the British lost 48. If the British forces weren't commanded by the most linear idiot, General Kitchener, to ever grace His Majesty's service, their casualties would have been probably close to zero.
Of course, it only happened once. The Sunni wised up and turned to traditional insurgent warfare over massed charges. err, "suicidal brainwashed volunteers". I never got people's well, almost frustration at the fact that our successful enemies use insurgent warfare. Saddam and the first Gulf War is the definition of 'crazy'. No country outside of Russia or China will ever pull that kind of war with us, except for the rare oddity. All future conflicts with small nations will be insurgent warfare.
Yea, you'll have the occasional true blue suicide vest. More often are car bombs. 2 suicide bombers killed 299 Marines in Lebanon. Much more often are remote detonations. The stupid and suicidal insurgents disappear in a hurry. The more patient ones can stick around for a while. IED's are the most efficient means currently employed by the insurgents. RPG's are a distant, but very significant second.
An interesting common squad based tactic developed in Grozy, Chechnya is 2 RPG gunners with a backup guy with an AK. AK gunner provides protection or acts as a decoy, while the two hidden RPG gunners wait until the last second. RPG-29's can turn even a M1 Abrams or Merkava into post toasties. Look up the beating the Merkava's took during the invasion of Southern Lebanon.