It's why they run the race in the first place. Worlds has a bye for prior champions - Olympics does not. We live in a "what have you done for me lately" world and Mu's fall was unfortunate. Olympics qualifying does not favor champions over anyone else - it's level playing field. Watching the replay frame by frame it appears that Mu turned her head to the left which likely caused her to move in that direction, and then her left leg may have made contact with Raevyn Rogers who was behind her.
Rogers, Huerta-Klecker, and Grace were thrown off the most by the fall. Grace ended up on the infield and had to maneuver the spot where two sections of rail meet in order to get back on the track. Those three had more of a claim than Mu. The fall took place in the first 200m of the race, but it was in the first 100m after they were no longer in lanes and breaking for the pole. For that reason the race should have been recalled similar to a fall in the first 100m of a distance race. They would have needed more recovery time for a restart but it seems a reasonable response to falls of this kind.