Why? It’s free, and it helps you, as the Amazon site says, share information about yourself with readers. While you can add static information about yourself (photo, bio), you can also a link to a blog and your Twitter account, so it’s not like once you’ve joined you have to keep checking in to keep content fresh (because hopefully you’re keeping your blog and Twitter fresh). Also available on your author page, you can add photos, video and tour events. Really, why wouldn’t you create a page?
How to get one? So glad you asked. Go to authorcentral.amazon.com and join! Plan on spending about 10 minutes setting up your page.