Question

why are the cabins of aeroplanes flying at high altitude pressurized

Answer 1

this is because there is already more pressure outside the plane and if there is no pressure inside then plane will crash due to more pressure

Answer 2

The cabins of aeroplanes flying high in the sky are pressurized as the outside pressure is way low than the inner pressure thus if this was not done humans would die as air would not be sufficient.

Hope it helps