Hi!
The reason for this is the code behind the contouring. CadTools use triangles in a very simple way. To calculate contours CadTools examine all planes for every triangle one triangle at time. This results in many contour polylines. This approach is faster than trying to find neighboring triangles.
If you would like to join them, look in the helpfile, Surface, Surface Contours and the bottom part “How to smooth the contour lines”
/Lars