It’s basic economics that a monopoly can charge more than firms in a competitive market. In the presence of competition, prices will be closer to cost. For a monopoly, demand still slopes downward as they raise the price, but they can set the price higher.

Collusion allows firms to get somewhat closer to the monopoly price.

I don’t how much this software really does to enable collusion, though? It seems like some landlords might defect if they have too many vacancies?