Now people know that the commission is negotiable, but first time sellers or inexperienced people were not aware that the fee was negotiable. The agent is not publicizing that his fee is negotiable. The agent may know but the seller most times is not aware.
To be clear, agents are not required to negotiate their fees. They have the right to set what ever fees they want, just as any business owner has this right. The consumer can decide if they think that those feels are worth paying for. The key is that different agents have different rates (this has always been true) and also the seller has the right to offer a buyers agent nothing or any number they wish. It is the job of the listing agent to help the seller understand the risks involved in how the chose to use this tool.