This is the point of dialectical materialism - before the 8 hour workweek there was an even longer work day with worse conditions. The people born into those circumstances struggled against capitalists (in the sense of people who have capital) to make 8 hour workdays the norm. The next generation was born with 8 hour workdays being standard, and capital pushed back and squeezed in other areas where labour wasn't resisting. Capital has now squeezed so hard that labour is organizing again and realizing they need to fight to retain any of their rights.