This has been considered rude at least since my parents were kids in the 1950s.
I would imagine it was a lot more common before the telephone at home was widespread, but I've always found turning up unannounced to be rude.
People did this all the time until txting was common. Once txt was common there was no reason to just drop by someone's place randomly without giving them a heads up.
Once the telephone was popular in the US this was something that people in our circle just stopped doing. All it took was a 30 second phone call to say "hey, can if I head over if you're not busy?" (and the answer was almost always yes, I'll agree that is likely different than today) to make sure, so that was considered the polite thing to do in our working class semi-rural midwest circle.
If you're living truly in a rural area where you're sharing a party line with others and the nearest place is over a mile away then yes, I'll concede, that was probably much more normal.
Of course there are some unwritten rules and some people that you do call ahead, but for many it’s still an acceptable practice.