As the article points out, the iPhone 13 mini sold half as much as the other iPhone 13 models, while competing with the iPhone SE which was the same size at half the price. That isn’t exactly terrible.
The relative preference for the larger unit has increased over time as well, e.g.: https://www.macrumors.com/2025/05/28/iphone-16-q1-2025-best-...
The articles are literally about how bad the sales were before Apple stopped making minis. There is no reasonable way to conclude that means they were actually worth serving.