That's unexpectedly low, I'd say. In SZ, the daily commuter count approaches at least 2.5-3 million for people living on municipality's border.

Shenzhen has twice as many people as Chicago. So, if we extrapolate, the amount of people commuting will double for Chicago if Chicago were to be turned into Shenzhen.

That tells that much, much, more people in Chicago work outside of urban centre, or the portion of population who is working is simply less.