Many wifi networks redirect non-encrypted http traffic to their captive portal. For the redirect to work, your DNS needs to be the default one provided by the router so that http://neverssl.com resolves to the wifi's "Please accept our ToS to get online" page.

If you aren't using their DNS, then your network requests just get dropped (as you're not approved yet). You need their DNS to learn how to access their captive host so they can whitelist your mac address.