Your post got me thinking. In fact, I haven't seen someone go careless personally in about 4 years. I will say that I have obviously not noticed every person and their phone that I've encountered. But, I do tend to look at phones that people have more than the average person does.
I am not saying going careless is incredibly rare. But my anecdotal evidence says that the vast majority of people use a case. The only people I've really ever seen go caseless (omfg my auto-correct keeps changing this word to careless bwahaha) are young people and then they break their phones a few times and start paying for their phones and then buy a case.
And usually that is young MEN. Most girls and women I've seen use a case because they are excited about a case and its design.
In any case, I don't have any judgement on anyone using or not using a case. I do, but it is pretty minimal because I want to get as close to not having a case as I can while still having some protection.
I went caseless for about one week one time with an iPhone 7. Fell out of my pocket onto concrete. Killed it. I've never gone caseless since then. The other day my 12 Pro Max fell out of my pocket and down the stairs. It was fine. That's the thing... I am quite careful in spite of my examples above. Nevertheless, I drop my phone about once a year.
And because of that one time per year I have to wear a case the other 364 days