You're leaving out closing costs which are paid by the buyer. They are typically 2-5%. The buyer is also the only one bringing money to the table, so they are effectively paying the agent fees as well. Those are generally 2.5-3.5%. So you are looking at 7-12% in total spent on the transaction.
If both the buyer and seller are using Redfin instead of a traditional agent, the buyer is paying all cash (some of the closing costs are a result of needing to get a mortgage) and the buyer is willing to take some risks like not getting the house inspected and not paying for title insurance, you might get that down to 3%. That's still a big chunk of money being spent on the transaction.