I'm in their income bracket of twice as likely and I do this as well. Not because I want to show off anything wealthy inside the house. Most things I have in the house are quite modest. I do it because I just don't care. To the point of I will walk around naked inside my home I really don't care. I'm not sure what other people's motivations are but I agree with their assessment that it does show a sign that people feel secure. I don't agree with their viewpoint that it's a way of showing off wealth.
Sounds like people feel secure, with law and order. The first thing you see in a less developed place is everything shut up tight. Even poor people have something that can be taken, like their children, or their bodily safety.
I’m visiting South Africa right now and this country feels like a military base. The amount of security, electric fences, and on-call “tactical response” vehicles is just bonkers. Needless to say, not many windows visible from the road behind 12-ft electrified perimeter walls.
From how SA is described, sounds edgy all right. Not the place you'd want to be seen in your/spouse/kids PJs through the front window.