I am going to politely say that you have not spent much time studying airplane accidents. The short reply is that if a plane is attempting an emergency landing, there will likely be wreckage that still resembles an airplane or components of an airplane because in an emergency landing the pilot is likely doing his best to lower speed and decent rate at the point of impact.
A 'crash' is very different, high speed, sudden stop, a lot more force dispersed over a much smaller time/distance. In the case where a crash has occurred, ie plane flies into a mountain, there is usually nothing left but a scattered field of small debris. Sometimes rescue teams can fly right over the crash sites and hardly tell it was a plane crash from just some random garbage on the ground.
The 911 plane crashes were high speed high energy impacts.
> ..... nothing left but a scattered field of small debris.”
He he he.