The process all along is about eliminating what is thought to be the weakest bid remaining. They put out an invitation for cities (metro areas really) to submit bids. An initial presentation is made to the IOC board, and they eliminate all but the best four or five. Those remaining cities are allowed to host tours and deal with delegates one-on-one.
Then about a year later they have a final series of ballots. After each round the city with the fewest number of votes is eliminated. Since Chicago was eliminated in the first round, that means it had the fewest number of votes of the four finalists, and was judged to be the weakest of the four bids. They voted again, and Tokyo was eliminated in the second round, and Rio won the final round of voting against Madrid.
Then about a year later they have a final series of ballots. After each round the city with the fewest number of votes is eliminated. Since Chicago was eliminated in the first round, that means it had the fewest number of votes of the four finalists, and was judged to be the weakest of the four bids. They voted again, and Tokyo was eliminated in the second round, and Rio won the final round of voting against Madrid.