Because your Realtor has to spend a lot of money to market your home (advertising- now extremely expensive, virtual tours, colored brochures (at 39 cents a page), signs, gasoline, costs of doing business, etc., etc.,) plus all the hundreds of hours of computer work, legwork,telephone calls, writing ads, delivering brochures to other offices, getting the word out about your home, keeping up-to-date with the entire market as well as the market around your home, etc., lots of work that is done in the background to get your home sold which you never see! Then, the Realtor - more often than not - has to share the listing fee with another realty company, plus give their own company its split (and some of us pay a 6% franchise fee to be a part of an international brokerage on top of that to bring more exposure and relocating people to your listing). Usually, if the commission is only 4%, the listing realtor will take only 1% - so that your property is more desirable for agents who may want to show it and won't pass it by because of the low fee. That leaves the listing agent with very little to work with -- so they cannot do as much marketing for you as they can if you list it for 6%. They simply can't, because the money is not there!
In today's market, listings are staying on the market longer and cost so much more to market ... and agents cannot work for nothing --or less than nothing, often costing them money out of their pocket to sell your home -- (I've had that happen!). Besides, agents find it hard to get excited about working hard for a seller who believes we are not worth the money we earn. The old saying: "You get what you pay for!" is still true in every walk of life! Would you like it if your boss asked you to take a pay cut to do the same job as the guy next to you??? You probably wouldn't work as hard, would you??? Enough said!