This is a really, really astute observation...it seems kinda obvious but it never occurred to me:
"The closest San Francisco comes to the small town feel it had from 1930-1981, is only on 3 days of the year. Thanksgiving night, the Day after Thanksgiving, and Christmas night. The streets are deserted. You can park in the front of any busy restaurant on Columbus in North Beach. Why? Because all the carpet baggers/dot commers from around the country and the suburbanites from the Bay Area (hello, Danville!)have all left the City to be with their families and SF is only left with the SF natives inhabiting it for these sweet 3 days of the year."