Why are you 'in' a movie, but you are 'on' TV?!
Question: Actually you are "in" a movie but "on" the big screen and "in" a TV Show but "on" TV.
Answers: Actually you are "in" a movie but "on" the big screen and "in" a TV Show but "on" TV.
Because you are in a movie that's showing on TV.
Very succinct and accurate answer Earth.
Earth beat me to the punch.