If you have chosen to sort a subfolder, or if you use an option like “always sort,” then I agree. But if you just happen to be at the top level folder, I don’t think subfolders should be sorted when you click “sort,” because they may be in an order that you want and sorting is an action that shouldn’t be destructive (unless intentionally destructive).

The sort button absolutely shouldn’t sort subfolders. I do think there should be an option to always automatically sort alphabetically, though