Back in the day, everyone did work 9-5 and had an hour for lunch that was considered on the clock. This was mostly due to the strength of unions in the 1940s and 50s. Businesses were reluctant to give in on wage demands and would make concessions on the hours in the work week and breaks/lunch etc. But back in the 40s and 50s, employee benefit packages were comparably cheap. Health insurance cost nothing. Pension plans were cheap as the majority of the participants were still in the workforce. So, companies did not mind hiring more people instead of having employees work longer hours.
Now, employers hate hiring extra people because of the cost and do everything they can to squeeze more productivity out of as few people as possible. Most every job now expects people to work 8 hours and does not pay for time off the clock at lunch. So, most everyone is in the office by 8:30, takes a 1/2 hour for lunch and leaves around 5:30. Some banks, Dr.'s offices and government jobs still keep 9-5 hours, but it is getting to be pretty rare.