If you did the same covering job, on the same part of a plane 200 times a day... You'd get pretty good at it too. It helps that the piece of covering is pre-cut for you, by a machine, to be the exact correct shape needed.

People who have done a lot of planes will do a better job. Its as simple as that.

The best looking planes aren't covered with film... they are covered with silk, or some other fabric (or fiberglassed) and painted by an expert. (They couldn't afford to do that with the ARFs...)