Why are you IN a movie, but you are ON TV?

In a movie you assume a character and have to be acting, but to be “on” TV, you don’t necessarily have to act or assume a character because it could be something like on the news. But other than that explanation, its just terms  used, English has always been a weird language.

You can be on tv in a movie.

Because am gazing on a screen to watch the movie which seems to be inside the TV.