On Github, when you create a project there's a setting for the license, and that setting explains if you don't set it the default is it's copyrighted and anyone wanting to use your source code would have to get your written permission to use it in their own projects. Which, as Github itself points out on this page, kinda makes Github pointless if everyone's code is copyrighted but no one sets a license (GPL, Apache, etc.) to allow for the use of their source code by others. I think generally it's automatic for creative works by a single person, but for a collaborative medium like film, you don't want it to be automatic. Otherwise the cameraman for each shot owns the copyright for that one shot and to edit the film together you'd need to purchase all of those copyrights. And all the cameraman did was operate the camera, what about the performance delivered by each actor, what about the lighting and the sound and the director setting up the shots and giving directions to actors?

Not everything one writes can have a meaningful copyright. Recipes, for example. Reproducing a recipe is considered fair use, it's just the instructions for creating something like a cake, it's not the creation itself. This is why recipes on websites are always published in the middle of long stories about how the recipe came to be known to the author and experiences the food reminds them of, because that story can be copyrighted even though the recipe can't. So if you write a license, that's just instructions for how a work may be used by others, that might not be copyrightable by itself. But if you write a book with fictional characters who as part of the plot need to come up with a license, and the text of the license is within the narrative of the book, then that might be copyrightable and no one could use that license in real life. I don't know, I'm not a copyright lawyer, but I know it gets pretty weird. If I create a song, and play it for a crowd of people, the lyrics and the melody aren't copyrightable, but the performance is. So someone couldn't record me performing the song and sell it, but someone could walk around singing the lyrics and the melody and eventually perform the song themselves (a cover), then perform that cover for others, and record their own performance of the cover and put it on YouTube. Because songs aren't copyrightable, performances and recordings of the song are. I think.