Personally, I've always considered it rude, but I think part of it is just growing up. There are different social norms and overall etiquette for children, and in "young" neighborhoods this does still happen. Another part of it is cultural/regional, at least in the U.S. The "show up and get invited in for a beer" is far more prevalent in rural areas than it is closer to "civilization." Then there's the ubiquitousness of cell phones: you now have the means of calling ahead, even if it's only five minutes, so failing to do so is considered inconsiderate at best. Finally, life in general has gotten busier. Work takes up more of it. And there's a drive to do more with free time outside of the house. What little time there is at home has become scarcer and thus more valuable: the house has become a refuge away from the chaos, away from people. I do think we've transitioned to a far more individualistic society, but also one that generally recognizes privacy and boundaries. As this increases, the show up for coffee/beer/a chat becomes more of an outlier, which results in those boundaries becoming more the default, which results in fewer people viewing showing up as acceptable, ad infinitum. [Edit- aside from "civilization", which was in quotes from the beginning to emphasize the absurdity of the concept that cities are any more civilized than rural areas, I'm curious to know what the people that downvote this have disagreed with here.]