I'm living temporarily in spain and notice something similar: they basically don't use the inner lane in roundabouts. So people go 3/4 of a lap on the outside lane which can be clogged while the inside is empty.
People tend to stick to the outside lane as they feel that if they go on the inside lanes they won't have the opportunity to move to the outer lane when they are near their intended exit due to other cars being on the outer lane.
IMO this stems from lack of education (driving lessons are not adequate) and the fact that everyone's looking after themselves (i.e not respect for other road users (which also explains the ludicrous speeds on the roads, road rage, queues, etc))
I hate roundabouts, at least partly for this reason. Whenever I'm taking anything other than the first exit, I'm moving round just praying that no-one's going to join or drive up alongside me...
(And don't get me started on driving lessons. Here, in the UK, they're an absolute joke!)
There's some of those in NL as well; I haven't learned any rules of those, so I can't be sure I can leave the roundabout on my exit if I'm in the inner lane, or if there's someone doing more than one exit on the outer / rightmost lane, making me cut them off.
This has caused me to shit a number of bricks in the UK, where two-lane roundabouts are a lot more common.
The general rule is that you should get to the outer lane once you are at the exit previous to yours. If someone stayed on the outer lane the whole time and you have to cut them off, it's their fault (obviously, you still have to pay attention and let them pass if you can't cut them off safely, but they are the problem, not you).
