[ChuckMcM]

That is an issue, there are a lot of different neighborhoods in both the US and the UK. So allow me to narrow my comment down somewhat.

In the San Francisco Bay Area and the Las Vegas metropolitan area, both places where I've been able to keep up to date on for about 30+ years, later neighborhoods have smaller lots and larger homes. In what started as the 'suburbs' in the peninsula like Sunnyvale, Campbell, Cupertino, and Los Altos. You can see pretty this pretty clearly from aerial imagery in Google Maps if you also know approximate neighborhood dates. We've had a number of towns propose or pass 'zero lot line' ordinances which restrict the building of residences that go right to the edge of the lot. And lots themselves have gone from 1/2 acre to 1/3 acre then to 1/4 acre, and now often 1/6 acre.

On the east coast, where I spent some of my childhood, back lots were commonly unfenced and effectively like mini-parks behind the houses out front, whereas in California fences are the norm. In Las Vegas fences are also the norm and lots have shown a similar drop although there was a lot of desert around so it has not been as pronounced as it has in the Bay Area.

My sister lived in Birmingham UK for a while and noted how much more invested folks she met were in their gardens than Americans were.