Football (especially college football) is popular because of the tradition (gold helmets at ND, the winged helmets at Michigan, dotting the I with a senior band member at OSU, the World's Largest Drum at Purdue, BeVo at Texas, UGa at Georgia, "Victory" at USC, playing for the Floyd of Rosedale (a pig trophy), the Brass Spitoon, Paul Bunyan's Axe, the Sweet Sioux Tamohawk, the Little Brown Jug or the Old Oaken Bucket in the Big Ten, singing your school's fight song and Alma Mater/Varsity) and a connection you feel to your team (I went there,too, this guy has the same major I had, etc).
Football is also exciting when play is going on and all eleven guys on your side of the ball have to do their job that is drawn up on the play for good things to happen play and there are some elements of the unexpected and luck to the game.
It's also great when there are Cinderella stories (Northwestern in 1995, Oregon State in 1999, Wisconsin in 1994, Illinois in 2001) or when one of the consistent winners goes down in a game they were expected to win (Oklahoma versus Texas earlier this year, Texas versus Texas Tech this past Saturday, Notre Dame versus Navy last year, Notre Dame versus Northwestern in 1995) to someone with poor history.
Everyone's played street football at the very least at some point.
Skating is not as popular because most people don't participate in it. It's seen as expensive and prissy (because of the sequins, crystals, and crying). If you've never participated, it's easy to mock.