To have others investigating not firmly under the thumb of the Executive branch might muss things up. And the President is now an experienced foot dragger, so why not push this out until there's some other event to distract attention? Why bother committing all the resources of the government to investigating the first jihadist attack on America since 9/11? After all, the FBI said this was not being looked at as terrorism, right after the attack. The attacker opens fire screaming the jihadist war cry "Allahu Akbar!" and it's not Islamic terrorism? Please ignore that man screaming "God is Great" unless he blows your head off. Then we're off to mourning mode replete with more odes to political correctness like our "our diversity is our strength." In this instance, our "strength" was a police officer pumping multiple rounds into a still-firing fanatic. Sanctimonious homilies are a tissue thin shield against terrorists.
The enemies of America are not stupid. There are very capable of learning lessons and applying them. The attack on the World Trade Center in 1993 failed, but the lessons of that failure paved the way to the horrendous massacre that was 9/11. They are watching and learning. Whether planned directly by Al Qaeda or not, this Ft. Hood slaughter enabled by a PC blind spot will be understood and filed away. Perhaps, it will give action to another plot immediately. Maybe it will give rise to another long term plot just as deadly as 9/11. Either way, a new weakness has been shown. They know it now, but the question is: do we know it? Will we ever know it?