I can't believe the people talking about discs as if they're nothing but a marketing gimmick have ever ridden a bike equipped with them.
There's a case for them on mountain descents on carbon rims in the rain. Not at Roubaix - unless its insanely muddy but then you'll have bigger problems. Strikes me as weird they even tried them there.
As for why - the team is using disc wheels in ALL their races. They had to adapt their cars and stuff to suit the new bikes so it's an all or nothing change to discs.
There's a case for them on mountain descents on carbon rims in the rain. Not at Roubaix - unless its insanely muddy but then you'll have bigger problems. Strikes me as weird they even tried them there.