Bulk/Spam is only queried of you click on the folder, while the inbox folder is queried always. If you press Shift-F5 all account are queried and all inboxes get emails if there are any - except the bulk/spam folders. Why is that? Wouldn't be useful to query them, too, when you press Shift-F5?
You surely know that sometimes even important emails land in the spam folder, and you wait for it and wait and wait… until you got it and look in the bulk/spam folder.