Are there really that many of them? I know many more people that work other than 9-5 than 9-5.
Most of the people I knew growing up were factory workers. Day shifts in factory usually start 6-7 and end 3-4 (plus many work other than day shifts.
In mine and my DHs military careers the day shift was either 7-4 or 7:30-4:30 (again many worked other shifts.
In my job now I usually work from about 7:30-4:15, DH's shift is similiar.
My DD1 either goes in very early and works until early afternoon or goes in mid morning and works until 6:00.
My DD2 is a teacher so does not work 9-5.
People I know in the medical field do not work 9-5.
People in retail and restaurants do not work 9-5.
I think that a 9-5 schedule is fairly limited to those working in offices and I do not know if office workers are a large enough % of total workers to consider their shift typical.