It’s all about preparation
Take these fenders, hood and trunk lid as an example. The metal is first etched with an acid etching primer to bind to the metal so following layers have something to stick too. This is the gold colored coating in the first pictures.
Over the etching primer we spray an epoxy primer to seal the car to protect the metal from rust. This is the black coating you see on the hood and fender.
The epoxy primer is followed by a high build primer, the gray primer in the last set of pictures, which fills any tiny imperfection and ripples in the metal to provide that perfectly flat and smooth surface for the paint.
All this preparation is expensive, time consuming, and down right hard work, but it is the only way to produce a finish that goes beyond merely good to become great, and is durable to boot.