I tried living in Chicago without a car… I wouldn’t say it is as optional as you suggest.
Chicago compared to anything not east coast is a life changing experience in terms of transit.
Yes, it's getting harder and more expensive. When I first moved to Chicago in 2004 though, it was cheap ($1100/mo for a 2BR apartment) to live a few stops from the loop off the blue line. That is rapidly changing, but still plenty of cheap transit-friendly locations if you're not super picky.
Really depends on where you live and want to be. This is true everywhere (NYC, SF, Seattle, etc.)
I spent many years in NYC and only knew 1 person who owned a car.
By contrast, when I lived in Chicago, I was the only person without a car.
I'll take the train instead.