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.
Thank you for being that sort of person.
I know some people who would take great pleasure in knowing that they would get paid for spending just that time, no matter if they achieved very little doing it.