According to the selection documents, they ask all Nationals participants to declare their interest in the TE, if they want to do zero, two, or one segment, and, if one, which one, by 28 days prior to Nationals practices. Which USFS reserves the right to ignore (the forms) and strong-arm the Olympic Team members into doing their bidding, but, ostensibly, not if they are contenders, and it would interfere with their strategy for individual medals, blah, blah, blah.
Then they rank the disciplines in the order of strength, and the Olympic team members in their order of strength, and ranking is based on a published list of international events beginning with the prior World Championships, with a whole list of criteria to magic eight ball who will be the strongest at the Olympics for both the individual and team events. (2022 was more complicated in declaring the competitions that would be considered, because they weren't sure if Covid would be a factor.)
They describe how the athletes originally declared might not be possible, like how by the time they get to the skater's/team's discipline, that skater/team would have to do both segments, because two disciplines above them split, or a skater/team ranked higher than they chose the segment they preferred.
Davis/White were the skater/team with the strongest prospects in the strongest discipline in Sochi for the US, and they chose to skate both segments, so it's not a slam-dunk on paper that there wouldn't be a split option left by the time the third or fourth discipline came around, especially if there was a dominant skater/team who was recovering from illness or injury.
Here's a link to the document for Beijing, where they got more specifically numbery: