Question

Why don't aeroplanes flying at higher altitudes cast a shadow on the ground?

Answer 1

The shadow of a plane is decided by
how much of the sun an airplane can cover

It depends on two things: its physical size and how far away it is from the ground (altitude). The smaller the plane or higher they fly = the blurrier the shadow.

So when planes are at higher altitudes , their shadows are blurry enough to be invisible on the ground...