Why need of Microsoft Account to download Microsoft Office?

You will need a Microsoft Account to download the software. Microsoft can help you set one up if you don't already have one. Microsoft can also offer MSDN and other subscriptions to Microsoft accounts. These subscriptions allow you to download any setups as well as get support from Microsoft for any problems you might have while installing the software. To install Office, you will need to have the product key. It might not work for one day if it isn't. For office subscription expired problems, you can also look here.