I'm wondering if there is not adequate preparation for competition, not adequate managing of training to prepare them to peak at Worlds. They all three peaked for the season at Nationals and apparently had absolutely nothing left for Worlds. That's a problem of preparation not relationship. And preparation can be fixed.
But that's what will happen if you make Nationals THE qualifier for Olympics/Worlds. The skaters will want to do their best at Nationals to get on the world team in the first place. Instead, if you make Nationals only part of the equation (i.e. send only the champion), that might ease the pressure a bit.
How about holding US Nationals in December instead, like most of the European countries and Japan? Or move it back to early January like it was before 2007.