When the person choosing the broker is the same one that pays, it creates competition on fees. The renter cannot choose to change the agent to a cheaper one. They have to deal with whatever agent the landlord has chosen.

It works similarly when software is chosen by people who have to use it versus those who do not. IDEs and text editors are usually chosen by the users, so there is competition on usability between different options. Timesheet and other HR software are usually chosen by upper management, and the people actually using them cannot switch, so there is not the same kind of competition on usability. Instead, they compete on other things that make them more appealing to those who can make the decision.