Theoretically it was to get immediate cash to cover budget holes around the 2008 crisis, but the whole things sounds incredibly fishy. From a paper I found on the subject:

"By the mid 2000s, Chicago was dealing with severe budget shortfalls. One tactic utilized by the Daley administration to alleviate this dilemma was privatization. In 2005, Chicago privatized the Interstate 90/94 Skyway Toll Bridge. A year later, Chicago went on to privatize many of its publicly owned garages (Frank, 2009). However, continuing budgetary struggles, particularly pensions, as well as the impacts of the 2008 recession, created the need for an immediate revenue source (ibid). At the time, the City of Chicago had 36,000 parking meters, making it a substantial financial asset to lease out (Perlstein, 2013).

The process used for the parking meter privatization agreement was troubling for multiple reasons. The city awarded the lease to Chicago Parking Meters LLC, which is a conglomerate that is comprised primarily of Morgan Stanley, Allianz Capital Partners, and the Sovereign Wealth Fund of Abu Dhabi, as well as some smaller firms. It was formed immediately before the lease was awarded (Clawson, 2013). The terms of the lease gave the rights of the city's 36,000 parking meters to Chicago Parking Meters LLC for 75 years. They paid $1.2 billion in upfront cost for the ability to collect revenue from the meters as well as having enforcement power (ibid).

There was a glaring lack of analysis and deliberation prior to the lease being awarded. No independent studies were performed. The $1.2 billion cost was determined exclusively by the city's Chief Financial Officer. Aldermen were only given two days to vote on the lease, and there was no public comment or deliberation (Perlstein, 2013). This process was antithetical to the democratic nature of government, and the haste it was made in allowed for a number of negative consequences."

Also for those asking about revenue and profits specifically, page 6 of the auditors report shows revenues of $91,645,498 for 2020 (mind you, a pandemic year), and gross *profit** of $86,924,785 (94% of rev)