Ending gun-free zones in Afghanistan

My only question is why it has taken so long for this change to be made.  It has never been obvious to me why US troops would have ever been disarmed within their own installations.  From The Hill Newspaper:

Gen. John Allen, commander of all U.S. forces in Afghanistan, has taken the drastic step of ordering all American troops to be armed at all times -- even when within U.S. or coalition bases -- as a way to protect against increasing insider attacks.
The order, according to reports by CNN, states that all U.S. personnel will carry a weapon plus a magazine of ammunition around the clock.
The weapons will be carried in formerly secured areas, CNN reports, such as U.S. headquarters in Kabul and other coalition and Afghan government installations around the country.
Allen issued the order on Saturday, a day after two members of a U.S. special operations group were killed by a local recruit to the Afghan police force in Western Afghanistan.
The two soldiers assigned to a U.S. special forces team assigned to train and equip local police forces in Farah province, were unarmed when they were shot and killed by Mohammad Ismail on Friday.
Their deaths bring the toll of American soldiers killed by their local counterparts to 11 in the past two weeks. . . . .