I use it almost daily when in bed and thinking of some project or the other—I like to think in text—but don’t want to bring up my notetaker and getting even more distracted.
And I often get friends and family open one up while troubleshooting their problems. What else would I use, Notepad?
Ultimately, why not? Why do people make little standalone tools like this? For fun, probably. Or because they can. As a learning exercise? And when it has no cost to the developer to maintain, or the user to use. Why would I even try to second-guess their motivation?