I was always being told to clean my room when I was a kid. It wasn’t because I was disobedient (actually the opposite is true); I was just naturally messy. I think it is the way some minds naturally work.
I can’t speak for all the messy folks out there, but my issue is once I know the outcome, I rarely need to finish. As such, I am ready to move on to the next thing. For a child, that means toys don’t get put away, craft projects are not completed and their room is super messy. For adults it means papers are not filed, lots of projects are in progress and the surface of the desk is only a distant memory. But there is hope for those of us that are naturally messy.