Prevents people from making more than one account and cheating with it, since the game is free (can not charge for something we do not own) so all we ask is you use your Internet provider / work / school email address, these can not be made and discarded like trash, like cheater would do.
Don't mind Bryce, that's not your main option at all.
Since you use Cox internet, they provide you with e-mail accounts; you just need to log in at the site and set one up. If you don't pay for the internet service yourself, you can either have the person who does create you an account, or you can ask to use their e-mail address and they can forward you the registration e-mail.
You only need the e-mail address for registration; after that, you can log in and set a free e-mail in your Account Settings.