Cancellara was always riding within himself and isn’t really renowned for needing a pile of teammates at the end of the classic races. I think most of Trek kept him safe for the first 200km then he was left to deal with the tactical part of the end by himself and the DS.
Sagan needed the help though and I think if Vandenbergh had worked with Van Avermaet a bit more he may have finished second rather than fourth but letting Cancellara and Vanmarcke catch them was a mistake. I guess they thought they might have a chance to get the others back to them for a bunch sprint but with the quality in that leading 4, it was unlikely.
Awesome race though, made better for me by the fact I rode the latter part of the course on the Saturday