Is it possible to combine two or more different apple accounts to one account?

No, you can't combine accounts nor transfer content between accounts - content will remain tied to the account that downloaded it.

Why!!!!

Ask Apple by using the Contact Us link located at the bottom of this page. We are users like you. We do not know nor can we comment on Apple policies.

Why should you be able to ??? When you buy/download something from the iTunes stores you are only buying a license to use it on that account, content is not transferrable to any other account.