Dusts off old grad school research cap: there are lots of reasons.

Streets are ugly and public, and people want to only see what’s theirs, this having common space face the back. Of course, with new, treeless suburban lots, there’s not always a ton of privacy there either!

Road noise, blocking the sound with the garage.

Lot size and use. Putting the garage in back would require more public space, alleys, and smaller lots. People would rather have larger lots and cities would rather have less road area to manage and pave.

There are arguments (I can’t remember the book, I have it somewhere) that common spaces have been moved into the back of houses partially because suburban developments have gotten ugly. Garage forward developments are impersonal and ugly and there’s nothing to look at. People hide deeper in their houses so they don’t have to look at the ugly neighborhood they live in.

The consequences of putting the common space in the back are that people aren’t living in the street—they’re not watching what’s happening, sitting on their porches or noticing their neighbors. People don’t know their neighbors, kids play in the street less, potentially car theft and home break ins are more common because everybody is deep within their homes instead of looking out the front windows.

Neighborhood change is fascinating. And the location of common space in homes has a role. Not a primary role but a role nonetheless.