Well Chris, I can't account for or know what other Tesla owners do with those public chargers. I can comment on why I've used public charging stations and used 110V at hotels and my sister's house. Sometimes, I need that 20 or 30 or 40 miles to make it to the next supercharger - or to give me enough buffer that I can relax while I drive. I do this when I'm traveling - like you guessed - never around home.
I don't plug into public stations around home or in the Chicago area. It seems like a silly idea. The charging stations are rarely where I want to go. So I'd have to park the car someplace inconvenient and then get where I need to be on foot. All that for some free electricity worth maybe a couple of bucks at most. No that makes absolutely no sense at all. The only way that works is if I could park for free in a good spot and be close to where I needed something.
In my 13,000 miles with the car - I've stopped at a couple of Nissan dealers to get 20 or 30 miles range (last Saturday was to get my battery warmed up, it was 29 degrees and the car uses a ton of electricity to warm up the battery), a BMW dealer overnight, 15 minutes on a Chargepoint station in Durango, CO, 110V at maybe 6 different hotels overnight, the dedicated charger in a hotel parking garage (one by valet and the other a self service area in the valet garage), 110V at my sister's house until she gets a NEMA 14-50 plug installed for me, and 110V at my cousin's house. Otherwise it has been all superchargers or Tesla high powered connectors.
Nope, I wouldn't ever think of plugging in at a public station in Chicago. Shoot, I can just drive over to the supercharger for free on Grand Avenue, if I'm going to mess around with public stations. I'd spend less time with that.
So why those people are plugging into a public station. I couldn't answer that question. I'd like to think they need the charge to get where they are going. No different than anybody else using the station.
As an aside - there was a long thread on the Tesla forum about how it was evil and wrong that somebody local would go to a supercharger and charge their car. Those are supposed to be for people on long trips and aren't for local people who want to charge their car for free. They need to get a charger at home and pay for their own electricity. At least that was the person's logic. What he missed in that twisted logic, nobody can know just by looking why somebody is charging their car or where they are from or what kind of hurry they are in. So get in line like everybody else and charge your car when it is your turn. We all paid to be able to use those charging stations - nobody is more entitled than somebody else.
I guess, you can't know why people have plugged in. It does seem unfair on the surface.