They technically dont, but if youre an engineer like me who is working full time, having someone work for you to do all the annoying parts of buying a house for free its a no brainer. If the seller is paying why wouldnt I use one?
Since you are paying the seller immediately before they pay the agent, "the seller is paying" seems like a technicality. In theory, if you could remove the seller's obligation to pay that additional 3%, you could get up to a 3% discount on the house.