Say what you want... but I think this, more than anything else,  BEST explains why Chicago didn't get the nod:

From ThinkProgress:

Bush Administration's Tourist Visa Policy May Have Cost America The 2016 Olympics

In spite of President Obama's lobbying efforts, the International Olympic Committee (IOC) may have chosen to reject hosting the 2016 summer olympic games in Chicago due to the post-9/11 visa tourist policies established by his predecessor, George W. Bush. Michael Froomkin, Professor at the University of Miami School of Law, is convinced that the "the same stupid anti-visitor policy that is destroying American higher education" also sunk Chicago's Olympic bid. Chicago was eliminated during the first round and received the fewest votes. A New York Times article points out:

In the official question-and-answer session following the Chicago presentation, Syed Shahid Ali, an I.O.C. member from Pakistan, asked the toughest question. He wondered how smooth it would be for foreigners to enter the United States for the Games because doing so can sometimes, he said, be "a rather harrowing experience."

A "harrowing experience" may be an understatement. Immediately after 9/11, the Bush Administration began requiring fingerprints and photographs of tourists from all but 28 countries entering the US. President Bush required that all foreigners register online within three days of travel. Thirty-five (mostly European) countries now participate in the US Visa Waiver program, however tourists from the rest of the world still have to jump through the following hurdles:

• Pay hefty visa processing and issuance fees.
• Undergo an interview by a visa officer at the US Embassy.
• Provide evidence which shows the purpose of the trip, intent to depart the United States, and arrangements made to cover the costs of the trip may be provided.
• Present convincing evidence that an interested person will provide financial support if the applicant does not have sufficient funds to support him or herself.

The average wait for a US visa has risen to about three months. Brazil, which will host the 2016 Olympic summer games in Rio de Janeiro, has a reciprocal visa policy with all countries. US tourists are required to have a $130 advance visa before entry into the country and are fingerprinted and photographed upon arrival -- matching US requirements for Brazilians.