I think we're starting to see a generation of drivers who nearly always drive on suburban roads or dual carriageways and very rarely drive on 100 kph roads without a dividing strip. They get freaked out when they do.
I see a lot of drivers who cannot maintain the speed limit when the road isn't dead straight and in some cases slow down when there is oncoming traffic. You can be sure they'll drive at or above the speed limit on straight pieces of road making it impossible to pass at a legal speed when it is safe to do so.
These drivers need to realise what they're doing and let other drivers past.