Cav gets boxed in on the left, with Morkov dropped somewhere around 500m... Whether that was because he didn't have the legs, or because Cav had been boxed in, not sure. Van Aert has a consistent leadout througout, while Cav is trying to get decent position behind him. Wout goes left from behind his leadout, which further boxes Cav in around 210m, then Cav has to freewheel around 140m, while Wout is starting his sprint. That, I think, is the killer.
DQT were properly fragmented on the run-up to the sprint, which came out of the stuff bees mentioned I think. There's an annoying cutaway at about 1km where he gets separated from Morkov.