Like so many things, this doesn't have to be the case.
The kerb shown here is one of many "forgiving" angled kerbs in use in Assen. These kerbs make it possible to cross from the cycle path to the pedestrian path without falling from your bike. They reduce the risk of injury due to a lapse of concentration.
Note that the rise is very small. Only a few cm. When taller angled kerbs are constructed, these do not enable safely mounting the pavement. Also note that the angle is important. If the kerbs are much steeper than 30 degrees then it becomes difficult to ride up the kerb without the tyres sliding sideways. This of course becomes a greater problem when there is rain or ice.
The video demonstrates how you can ride up and down the kerb without losing control of your bike.
This kind of innovation makes the cycling environment very forgiving of errors, and keeps down the injury rate of cycling. It is one of the many very small details of the Dutch cycling environment which add up to it being very safe overall - the concept of making the road environment more forgiving of error is called sustainable safety.
|These kerbs make it possible to take a bicycle onto the pavement when there is a lack of space, such as here during a cycle racing event (the road is being used for the race, the cyclists on the cycle-path are going slowly)|
|In the city centre, cyclists can easily access cycle-parking facilities because of the kerb design.|
|Finally, an example which doesn't work. This is too high and a little too steep. It's not possible to ride up this kerb. It's a good example of drain treatment, though.|
"Parallel" refers to the kerbs being parallel with the direction of travel. Even a very small gap can cause cyclists problems if it is parallel.