The police have managed to reduce suicide bombing attacks in Afghanistan, by going after the few crews that organize and carry out these attacks. Recently, for example, arrested 17 of 20 members of a gang that had carried out six bombings in the capital during the last two years. These attacks killed twenty civilians, and this played a large role in identifying the gang members. Most Afghan civilians are hostile to suicide attacks (it's seen as an Arab perversion), and that led to enough tips to finding who was behind the bombings. The three who escaped, probably to Pakistan, where this form of Afghan terrorism came from. Meanwhile, the number of suicide bombings declined from 2007 to 2008.
Al Qaeda began using suicide bombers in Pakistan six years ago, and the terrorist organization was promptly taken apart by an enraged Pakistani government, with much public support. This, despite many Islamic conservatives in the government. Al Qaeda was largely driven out of most of Pakistan, and confined to the tribal areas along the Afghan border. Here, the Taliban had a lot of influence, and al Qaeda convinced the Taliban to support a suicide bomber campaign in Afghanistan. By late 2006 and early 2007, there were a dozen suicide bombing attacks a month in Afghanistan, over fifty percent more than in the previous six months. This campaign was even less successful than previous ones. The Afghan Taliban do not have the experienced support personnel (bomb makers and bomber handlers) to make most of the attacks successful by any measure. Meanwhile, most of the victims are Afghan civilians. Naturally, Afghans see these foreigners (Afghans are difficult to recruit as suicide bombers) as murderers who do not have Afghan interests at heart. In 2008, some of the suicide bombing experts (bomb makers, trainers for the bombers) moved back to Pakistan, where the Taliban was under increasing pressure by a Pakistani army that had invaded the tribal territories.
Suicide bombing is described as a weapon of the weak. What it cannot be described as is a weapon of the victorious. In the last few decades, whoever used suicide bombers not only failed to gain anything, but saw their cause harmed in the process. You can draw your own conclusions, as have most Afghans.