If you have desperate people they will be willing to work for next to nothing. You can have them performing valuable work that adds value that customers pay for and the owner keeps the profit.

Even better is when you have different groups of people in poverty who you can use as labor pools, you can try to manipulate them or pit them against each other… anything that keeps them destitute will benefit capitalists.

To address your question, you do need multiple classes. You wouldn’t try to bankrupt the upper middle class if you have long term plans.