I rather buy the idea that the secondary explanation is actually the primary reason. In the first picture you can clearly see such a structure in a corner that

I rather buy the idea that the secondary explanation is actually the primary reason. In the first picture you can clearly see such a structure in a corner that doesn't connect to any kind of street/alley. Thus, I personally, don't buy the primary reason. Of course, unless that specific spot was made much later in time.