It’s not limited to TV shows, there are also pilot experiments.
If you’re asking why is the word “pilot” used, the dictionary lists one meaning as “a piece that guides a tool or machine part”, so maybe the idea is that the pilot will serve as a guide for the potential of the show? To see if it “flies”?
Note that one definition is “a television show produced and filmed or taped as a sample of a proposed series”, so it’s safe to say that it’s standard.