I don't see why scripts can't write themselves, kind of like player pianos. Some scripts sound like they've written themselves. But if a script were to write itself, I would think it would not want to reach an ending, as writing its end would be not unlike commiting suicide, which is an entirely troubling philosophical problem for a script, especially if it's an Adam Sandler script and therefore not particularly sharp in the first place.
This must be why scripts don't write themselves.