herethereeverywhere - the rules of society and class distinctions were mainly enforced by economic necessity over centuries.
For example. In Victorian times the gap between rich and poor was extremely wide. However, there wa s very little welfare state back in Victorain times so anyone who was poor, who had no land or property and no real professional skills found it beneficial to go and work in 'service' as servants for wealthy people. A roof over your head, food on the table, clothes on your back and a steady job for the rest of your life was something many people were happy to grab with both hands as the alternative was work in a grim factory or living in a workhouse.
The economic facts of life reinforced the master-servant relationship in Victorian times but nowadays the welfare state means fewer people are willing to endure the strictures of servant life. They have an alternative.
After WW1 the class structure began to collapse as the cost of the war meant many families became a lot poorer. Many gave up their servants. There was a further economic collpase in the 1930s and a further collapse after WW2. Far fewer families had live in servants as a result.
Having said that, nannies, cleaners, house keepers, cooks, chaufeurs, butlers are all still present and increasing in numbers in London as the gap between rich and poor is now as wide in London as Victorian times and many immigrants are willing to work that servant life.