In this 15-minute video, John Hess gives a terrific overview of the history of the screenplay format, and how changes in the film industry changed the way the words are arranged on the page.
I could quibble with a few things.
First, the modern screenplay has an obvious analogue in the stage play, and didn’t develop in a vacuum. Second, Hess gets a little proscriptive at the end of the video, and conflates screenwriting software with the format. (Which is part of why we made Fountain, to untangle the writing from the formatting.)
But his overall point is worth making: the screenplay format is what it is, and it’s a fool’s errand to try something wildly different.