I don’t really ever leave my house and I live in loungewear. I ain’t changing just to go to the store. That’s a ridiculous waste of time and energy. I don’t think that most Americans care what other people think about their clothes.
I have seen this on very few occasions, and each time, the pajama-wearing individual is very obviously only out in public so they can either stock up at the liquor store or meet their meth dealer. I don't think this is common.
I had coworkers in the early 2000s who would do this, working in a white collar profession, and pretty sure they weren't alcoholics or doing (hard) drugs.
They didn't wear pyjama's to work, but they did wear them out of the house to go buy snacks or such. Also, a number of us didn't normally wear suits or ties to work, especially if we were technical and not sales or administrative. This might have been due to not being in Canada. I did a few weeks in Toronto, and a number of guys followed the same rule.