In January, I visited my friend near Washington, DC, where he owns a very expensive house. It was not a small house, but it was an attached house. But it was a very well designed attached house. With a detached garage, which was attached to other garages.
It is easy to forget that the Ranch or Rambler house of American suburbia was (in its time) quite an innovation. Historically, most garages were not attached. For the narrow and deep lots of streetcar America, it was impossibility. So most garages were alley access to the rear, and many were little more than sheds. Putting the garage and house under a single roof was quite an innovation.
In most of America, attached housing still labors under a stigma. It is still second-class housing, for people unable to afford better. But I wonder--would more people accept attached garages? Were a developer to detach garages from houses, and then attach the garages, would the result be a saleable product?
Perhaps. But it would have to be well designed, and designed in such a way to reduce the amount of land area devoted to roads. The size of an average two-car garage is 400 SF. Detaching them from houses and aggregating them doesn't change the actual number of SF of ground area used. The size of an average two-car garage is 400 SF. Detaching them from houses and aggregating them doesn't change the actual number of SF of ground area used.
There is a reason that apartments have parking lots rather than individual garages. Rather than having individual driveways accessing individual parking lots, there is a single driveway accessing multiple parking lots. But that also constitutes a loss of square feet to the owners--a driveway is still usable living space.
To make it work, the garage clusters would need to be peripheral, located on the edge of the development. Yet to maintain the garages as personal and private space they would need to by connected to the homes. This suggests a cul-de-sak format, with garages arranged around a bulb that has ready access to the roadway.
Not an attractive urban pattern. And thus not an efficient development pattern.