The reason is simple, the look and especially a robustness that made the success of the brand! Indeed cab and dump are covered with folded good quality paint metal!
The chassis and the wheels are very sturdy and thick plastic, so this toy seems indestructible compared to others, it is not uncommon to see models that have several decades.
In view of its size principallement it will be used for outdoor load soil, rocks or whatever you want! Really simple toy that dévelloppera the imagination of your children (from 3 years)!
Note that there is a whole range of these vehicles including a backhoe of equal quality!