Really, I was just curious about this. I have been looking at one way flights from Warsaw to Paris. I started on KLM, who offer nonstop flights operated by Air France and flights with a connection in AMS operated by KLM. On Air France, I can of course book those nonstop AF flights (not sure if they had the KLM ones). Out of curiosity, I tried Delta, and they don't offer one way flights at all on that route. If I try a round trip ticket, they only show me the KLM ones, not the nonstop Air France ones. Obviously, I can book on the Air France site if I decide to book, but I was just curious why Delta doesn't have either the one way flights or the nonstop flights. I always figured you would see the partner airlines flights as well, but maybe you need to search all the partner airline sites to see available flights.
Thanks for any info.