Greed and distrust are the reasons. Buyers think that they can save commissions by dealing directly with the listing agent, when in all realty, they will be paying the same, without representation and the listing agent is probably receiving both sides of the commission. Some also have a very low opinion of realtors. Perhaps they have been burned by a bad agent. It happens. It is our job, as professionals, to educate our buyers so that they know that it doesn't cost them money to have realtor representation; it costs them not to have realtor representation. Also, we have to demonstrate, with our knowledge and expertise, that we can be trusted.