What's wrong with Taylor Swift winning? Drug soaked hippies just being mad that a pop/country song can top their holy grail of lists.
Other than that it is a pretty bad song nothing really strikes me as justification for preventing it's victory.
BTW here are the previous winners of the contest
1993: Dennis Leary - Asshole
1994: The Cranberries - Zombie
1995: Oasis - Wonderwall
1996: Spiderbait: Buy Me a Pony
1997: The Whitlams - No Aphrodisiac
1998: The Offspring - Pretty Fly for a White Guy
1999: Powderfinger - These Days
2000: Powderfinger - My Happiness
2001: Alex Lloyd - Amazing
2002: Queens of the Stone Age - No One Knows
2003: Jet - Are You Gonna My Girl
2004: Franz Ferdinand - Take Me Out
2005: Bernard Fanning - Wish You Well
2006: Augie March - One Crowded Hour
2007: Muse - Knights of Cydonia
2008: Kings of Leon - Sex on Fire
2009: Mumford and Suns - Little Lion Man
2010: Angus and Julia Stone - Big Jet Plane
2011: Gotye - Somebody That I Used To Know
2012: Macklemore - Thrift Shop
2013: Vance Joy - Riptide
Some of those are okay. Some of them are terrible. But it is pretty hard to make a case that any of those songs are the best from their respective years and Shake it Off would not be out of place on that list.
EDIT: Having said that I have to admit the all time lists are at least closer to what are actually the greatest songs of all time.