Yup you are right , they are handed many of the difficult bits in a plate and they just have to pitch.
But frankly, such controlled environment ability based tests are done to assess the specific ability of that individual. For example, if they send off people to find their own sales from scratch, it will complicate the assessment process coz then every sale will have its unique situation , some making it simple , some making it harder and that wont be fair to the participating candidates . Hence in a controlled environment when they pitch to , more of less the same the same people , that is when one gets an absolute idea of how various candidates react in the situation.