Facebook's IPO didn't happen until two years later and isn't mentioned anywhere in TIME's POTY article. So I doubt that has anything to do with anything.
Meanwhile it was the year of "Collateral Murder" and the diplomatic cable leaks; it was arguably the year Wikileaks went from unknown to notorious.
Assange was at least in part resisting a possible extradition to the U.S.
More than 'in part'. It's the entire reason. He has stated he will go to Sweden to answer the (really obviously trumped-up, btw) charges if they will guarantee he won't be extradited to the US. Since the reason the Swedes want him in the first place is so they can hand him over to the Americans, obviously they have declined.
My mistake for taking 2011[1] from higher up in the thread rather than checking the magazine itself, which as you correctly point out gave Zuckerberg the award at the end of 2010; Wikileaks' peak. I still think controversy over the rape allegations at the end of the year did more harm to harm Assange's chances of nomination than damage he did to US govt interest since "the Protestor" (including specific Occupy references) won the award in 2011 and Putin a few years before. They've been pretty consistent about ignoring poll results too.
[1]Irrespective of whether you feel Assange was trying to avoid a hatchet job and rendition to the US, justice or something in between, 2011 was a bad year for him. I don't think he'd disagree.
Meanwhile it was the year of "Collateral Murder" and the diplomatic cable leaks; it was arguably the year Wikileaks went from unknown to notorious.
Assange was at least in part resisting a possible extradition to the U.S.