Earlier quoted context omitted.
That's great for you, but I'd bet no one else can effectively use your scripts. The beauty of the UI is that anyone can use it almost immediately.
Why does this matter? There's no obligation to always make software useful for other people. There's a lot of space between doing something manually and selling a product.
The problem, which you basically acknowledge, is that software that isn't useful generally doesn't get used. If you write nice custom scripts to make your own workflows more efficient, that's great... for you. But to make any interface "useful" (whether it's a UI, an API, etc.), it doesn't just need to be "useful", it also has to be accessible. That should help explain why even crappy UIs are so ubiquitous. They are moderately useful, but extremely accessible.