Oh put your tinfoil away for a while. It'd be far easier for NASA to jump to the foam explanation, make some "fix" and get on with it. They're doing due diligence by looking at other possible causes -- so as to get at the real cause -- whatever it is.
I disagree with your assessment.
NASA dropped the most obvious cause - a huge piece of the tank's foam hitting the left wing - on the day after NASA said they were considering it.
Then we immediately get one BS cause after the next: Meteorite. Space junk impact. Sprite. These would have only be part of actual DD if NASA brought these up for consideration at the same time as the foam. It's too late, especially now after NASAs attempt to bury the foam problem.
What is the difference between The Foam Cause and all these other "possible causes"? The foam pins the blame directly on NASA incompetence, the other causes release them from blame.
The cat's out of the bag. The 1997 report by NASA engineer Greg Katnik is a virtual indictment of both NASA and their PC foam.
The official final report cited faulty booster rocket O-rings and the media dutifully reported it with no questions asked, which is a total joke. If you operate equipment outside of their design parameters, it isn't the fault of the equipment or the designer when it fails. The real cause of the Challenger accident was gross mismanagement. The NASA brass does not want that to be the cause of Columbia's loss, too. That's why they're trying to find a magic bullet to blame the accident on.
When NASA implies that meteor collisions and sprites are more likely causes than the big piece of insulation that was filmed hitting the wing that failed later, what does that tell you?