It doesn't, it gets you into the wifi network's login portal, from which you can log in and then ssl will start working.

[Edited to add] The problem is that websites that require ssl prevent you from getting into the login portals.

I have http://detectportal.firefox.com bookmarked on my phone for this exact reason.

Some WIFI networks require a login like airports or hotels. When you use https sites it wont redirect to the proper “wifi login” page as it should. This site being http should redirect you to that “wifi login” page

Some wifi networks will display a login/payment page to you by mitm'ing your connection & replacing the page you tried to load. But of course this only works for HTTP pages.