You probably have your magic wand setting too fine.
This setting controls the precision of curve conversions.
However, if you are in the process of converting a site plan into a 3D terrain, contours are a bad way to do it. Contours are themselves interpolations of other data, so don't get caught up in their sinous beauty.
It's a trick! Efficient site modeling is an art:
It is faster in all ways, drafting and imaging, to impose a 5x5 m grid (finer or coarser, depending on the steepness and regularity of the site) and only plot the grid intersections. If there is an important outcropping, you would add nodes at that place. Smoother areas could have even fewer nodes.
Dwight Atkinson