I'm reminded of when I did FSBO years ago for my home. Interestingly, while I didn't pay a listing broker, I did offer commission to buyer's broker. Otherwise people just weren't showing my home.

Apart from all that, lets assume a buyer has their own agent representing them. If the commission isn't being paid through the MLS listing at closing, then the buyer has to have the cash to pay their broker. They won't be able to work that in to their financing. That will also limit the buyer pool.