It used to be that you could have a yard with your house no matter where in North America you bought it. Cities, towns, it didn't matter. We had so much room that we could afford to waste parcels of land in urban areas on patches of grass. While we still have a lot of room on the continent, most of it is between cities. The cities themselves have expanded and their populations have boomed, lots have been split and split again to hold more and more houses so that today city yards are super expensive. Space is sold at a premium.
The supply of back yards in big cities is dwindling at an alarming rate as the lots get split up and no new backyards are springing up to take their place. They're not even included in most home designs these days because there's so little room to work with as it is that yard space would be put to much better use as a bedroom or kitchen. So back yards are becoming increasingly found only in the suburbs outside of the city and the inner city neighborhoods are building up vertically, with single-family homes giving way to towers of condos, taking land that used to be occupied by abandoned factories and businesses.
Because of the increasing land values in cities and the resulting scarcity of back yards, back yards' roles in our lives have changed. They're no longer informal and practical. You won't find many children's swing sets, derelict old cars, and clotheslines full of wet clothes in city back yards. When you do see city yards they're dedicated, professional backyards, devoted to one activity and one activity only, and it's usually entertaining. People are so used to living in condos that they would be scandalized at the thought of wasting their valuable green space on a play area for the kids when there's a park down the street.
People who have back yards in the city these days are generally regarded as either really rich or really lucky. You have to have been really lucky to find a place with a yard at all, much less a home with a large lot. The only other time you may encounter a home with a bigger yard than most is if that home is from a neighbourhood with much older homes. Properties built years and years ago still retain the big yards they were built on if some developer has not yet made an offer on the land.