The network that carries the Olympics buy the rights. They paid over a billion dollars for the exclusive rights. After getting the rights
they then have complete control of the event. They won't even allow the other channels to post the highlights of the events. In fact there
was a joke going on on one of the other networks. I am not sure now which one it was. But they made up the swim competitions with puppets, made out of popsicle sticksn in a long pan with blue crinkled up foil, with water in it. They then would voice over the thing as they pulled the puppets along telling about the distances and times.. Pretty funny, unfortunately it was a bit true and sad at the same time.