Because only a few fortunate users gained early access in beta mode. In October, Pottermore will open to everyone, but in the meantime only those users who could register can access Pottermore.
Wait 'til October when the site opens to the public.
You see Pottermore held this 'magical quill' contest and those lucky users gained early access. Dont feel too left out though a good lot of us, including myself, havent recived our welcome emails that offically allow us into the site yet!
