I would not say that this only applies to monopolies. You could add in companies that have strong moats, companies and industries that are able to collude(real

I would not say that this only applies to monopolies. You could add in companies that have strong moats, companies and industries that are able to collude(real estate brokers). Essentially there is more room for profit as competition decreases, but it is a sliding scale and not only monopolies apply. Even in spaces where there is lots of competition, it takes time for companies to reduce prices closer to production costs, aka a race to the bottom.