I agree. Stories should stand on their own. You described the reason it's so frustrating very well. And yes, in terms of books, it does feel like a ploy to buy the next one.

This story does stand alone nicely. It leaves a lot of open questions, but in 50-word stories, that is quite often the case. There is something really interesting and sad going on here. We may not not fully grasp what it is, but we do see the complexity of the relationships, the fact that a life is ending, and that the person who is leaving this earth believes the other person to be at fault.