Realtor here. Basically realtors are paid to close the deal. It's like any sales job, no closing, no payment. The problem with most FSBO is that they are trying to save the commission for themselves and because they don't know the process, it's a lot more difficult for both buyer and seller. There is also the matter of trust, buyers and sellers typically don't trust each other and both parties can get a little nutty so if there's a 3rd party, one side can talk the other down, otherwise both sides dig in their heels and it's no deal.
Also don't forget where the money for apps come from. Did you know Zillow makes money from real estate agents that advertise on their site. Guess where real estate agents get their money from, commissions. Eliminate the realtor and you eliminate the income that allows those sites to be created.
And you do realize what site we're on, technically all those quick change oil lube places should be out of business as changing you own oil is easier than a real estate transaction.
There's also value in being able to plug into a ready made network. I recommend home inspectors, attorneys, insurance companies, mortgage brokers and I also have a list of electricians, plumbers, HVAC, etc that can come in handy after the sale.