Originally Posted by xliioper

It may be due to historical business flying fare discrimination practices. Business flyers often book multi-city trips to visit multiple clients and in most cases they will likely need a layover of more than 4 hours to visit a client (thus creating a fare break). Cheaper fares can also have fare combination restrictions (such as requiring A-B-A routing, aka a roundtrip). This also serves as a form of fare discrimation for less price sensitive business flyers on multi-city trips.