Ive taught scheduling at both the bachelor and gradute level and have found the WBS concept and identification, the hardest subject for engineers and architects to grasp.
In our country, most contracts are unit cost, not lump sum. And both agencies and contractors tend to visualise projects in a one-dimensional mode: cost.
Therefore, the only structure they understand is CBS. Besides, the CBS in a unit cost contract tends to group similar tasks under a single tag, regardless of space and time. Any square meter of brick layed goes to the same bag, no matter where or when it is layed.
WBS involves cost, space and time and demands a wider view. In my opinion, understanding the difference marks the line that separates project managers from contractors.