McCool didn’t come off the beam, she had a wobble on her Onodi but otherwise did basically the same routine she did at Nationals and Trials but the Olympic judges weren’t as generous with crediting skills that weren’t all the way around and slow connections. (Also the wobble on the Onodi meant no sheep jump after.)Courtney Kupets was expected to deliver. She was supposed to do beam. She didn't. Even Carly didn't deliver as much as she could have for the team. Courtney McCool came off the beam, when it was supposed to be her best event and she was expected to be a rock.
It would be interesting if Patterson had hit beam at Trials and had one of the two automatic spots rather than McCool, whether McCool would have been selected for the team at camp or whether a bars-beam specialist like Memmel would have been chosen instead (I assume it would have been Memmel over Vise since Memmel got the alternate spot.)
And Kupets had what turned out to be a torn hamstring so it’s not like she didn’t do beam because she didn’t perform in prelims or because she didn’t feel like it. They downplayed the injury at the time and just called it a strain because that’s what you do with the Karolyis but in later articles she said it turned out to be torn.