The results are from the omnium, so people target certian races, and others have their weak point.
Once a rider, or in this case two, gain a lap and get back in the field it is very hard for a large group to gain a lap on them. Usually what happens, if there is time, another rider or two will go off the front and try to gain a lap to join the top two that are already up a lap.
The best way to look at this is not to think everyone is down a lap, but that Dibben and De Buyst are up a lap.