3828495 - Why are One-way fares for the same itinerary cheaper than the Round-trip and Multi-city airfares?

I was searching for an airfare, selecting Round-trip or Multi-city searches, and SAP Concur displays a higher fare. The same search is requested as One-way flights, then SAP Concur returns One-way lower fares. Why are Round-trip and Multi-city airfares higher than when selecting One-way flights and fares?

Round-trip and Multi-city fares in SAP Concur are higher than when booking as One-way fares. , KBA , CON-SRV-TRV-ADM-LAN , View Airlines , CON-CA , Cross Applications , Problem