I would also like to understand why this limitation exists. It seems we should decide where attachments can be made. for example, my customer wants the attachments to be related to a particular section of the form. Attaching them in the attachments tab does not allow the attachment to be associated with any particular area of the form.
Excel Sheet #1 attached supports Section 1 of the form.
Excel Sheet #2 attached supports Section 2 of the form.
Attaching 2 excel sheets in the task attachments tab doesn't allow for any association therefore we cannot automate anything on the backend without implementing a naming convention which is error prone and inconvenient.