The advantage is to the airline is to stop you from circumnavigating the globe on the fare. Also to control how you can route, limit the number of carriers the airline needs to share the money with etc

Even if it was unlimited transfers, there are other limits in other parts of the fare rules that would stop you from adding on to the fare. For instance Routing rule, Maximum Permitted Mileage (MPM), date restrictions, end on end ticketing, Maximum stay, minimum stay, carriers allowed to operate etc

The only advantage with transfers is on an international itinerary a transfer is considered a stop of under 24 hours so say you can stay long enough to visit a friend for lunch or if you just want to see a new city or stretch your legs, take a nap etc

Stop-overs are completely different