If you have certain number of articles in a main category, once you create a subcategory with different articles in it, the subcategory appears in between the articles from the main category. The user expectancy is subcategory to appear at the top, right after the main category. If you have a big number of articles in the main category and you want to reach the subcategory it requires unnecessary scrolling and also add confusion to the main view. Example screenshot attached below.