Why/How did the parent product category get added to certain products/services? We'd like to remove these sub-categories but QB won't allow this.

KimAnnVA is right, k-myers1. We can remove the sub-categories within in your QuickBooks Online (QBO). I'll further explain this in details.

Before we proceed, could you please let me know the error message you've encountered that prevents you from removing the sub-categories in QuickBooks? Any additional details and screenshots would be greatly appreciated. 

When creating the Category in the Products/Services menu, the parent product category gets added if you ticked the checkbox and assign a parent category. If you want to remove this, we can do so by going to the List menu. 

Here's how: 

1. Sign in to your QuickBooks Online account.
2. Click on the Gear icon, and select All lists.
3. From there, choose Product Categories.
4. Select the specific parent category from which you want to remove the sub-category.
5. Click on Edit, then unmark the checkbox.

Additionally, QBO makes it easy to keep track of your product and service items, allowing you to generate more detailed financial reports and conduct transactions more efficiently. You can learn more about this through this article: Add product and service items to QuickBooks Online.

Feel free to reach out if you have any other questions or concerns about managing your categories in QBO. We're here to assist you. Have a great day!