This has been the scenario on many occasions since the dawn of time. As soon as one guy gets a gap, the chasers start looking at each other because nobody wants to do all the work so somebody else can profit of that. If one of the favorites in the chase still has domestiques, everybody will look at those guys to do the work. Obviously those guys are not better than their leader, and their leader already wasn't good enough to follow the guy who attacked to begin with. So basically the entire chasing group is counting on guys who are nowhere near the level of the guy in the lead, in order to close the gap. So then you get a few halfhearted attempts to close the gap, but as soon as somebody sees others in his wheel, they stop because again, they don't want to drag others to the finish while doing all the work. And then there is a guy like Van Aert who under normal conditions will win the sprint, so nobody feels inclined to work even more because they'd just be working for Van Aert in that case.