The orange peel comes from the electrophoretic dip the cars first receive in the painting process. The amount of paint is controlled by the current applied to the shell through the carrier, and different metals react differently to this. So bodies with aluminium sections, galvanised sections and mild steel sectiosn react very differently. The higher the current the more paint is applied, but orange peel takes over then. In some ways orange peel is good. !
Some of the orange peel is reduced by the primer coat as this acts as a slight paint leveller, but can't cope entirely. Then the colour coat follows the primer surface and the clearcoat follows on again.
I've seen some pretty exotic motors wet samded to remove orange peel (Rolls Royces included). You need a heck of a thick clearcoat to remove orange peel these days, normally only the multiple layers of a Bentley/Roller etc have sufficient thickness to fully remove it. Wet sanding thinner paint films results in breakthough of the clearcoat and a respray
