As a learning exercise
As a labor of love
To scratch an itch
To explore an idea
Many reasons
that by no mean is a bad thing, it just means doing things for themselves, to express, to learn etc, typical of creative work.
People do that all the time. However in OSS there is this thing when people feel they need to present their work as useful to others eventhough clearly what drives their work has nothing to do with other peoples' needs, it's just their itch.
Remember that one of the original motivators behind "Open Source" is scratching your own itch.
that's what I said, and you repeated it, as if it's some new insight or supports some argument.
Is there not an issue in OSS where thing that should not be used in commercial context, are used in commercial context, they break, then people blame the adopters for expecting too much from OSS? Rarely the other side of the coin is addressed which is creators (not all of them) went out of their way to promote adoption of these things.
Here is an analogy: art design chair sold as office work chair. Of course if you are smart you would not buy them because over time the ergonomic would kill you. But that doesn't mean no one would. When some gullible people buys these chair, you say: idiots. However, I bet you also think about the people who made these chairs paid for TV commercials that never show the ergonomics of the thing, and question their responsibility.
Now replace "art" with "hobbyist software"