Because, by the evidences which the have, I think it could be hijacked by the 30 years experienced pilot. I suspect the pilot... Who knows? It may have been crashed into some mountains and the pilot could have escaped somewhere. And also, I do not believe that they will ever find the airplane....
I don't know if this is a fact, but I think it is highly possible that the air plane flew into another dimension. It disappeared and we don't know where it went, just like the planes and ships at Bermuda Triangle.
I don't believe terrorists hijacked it, because they would hijack it into something,
also I don't believe in 911, I think the Archons were behind it.
I don't believe in Terrorists or Al Qaeda, I think the Media just uses them as a cover up for the real phenomenon,
I think it could also be possible that a death ray experiment was going on and a death ray may have shot the plane down?