Even if you don't accept that who was in government had anything to do with it's actual passage, you realize that the law itself could have been written a thousand different ways that were less favorable to the workforce if politicians on the other side had their way.
Many of these jobs were 6 days a week, from what I understand. Could have easily been that a 45 hour workweek became the norm if others had been in control of the government. Maybe you would only be guaranteed one break on your shift instead of two.In the early part of the 20th century, the majority of Americans were working a 12-14 hour workday, regularly.