The highest ranked factor is put at the top of the list to emphasize its importance and prioritize it over the other factors.
In this particular case, the instruction is asking you to rank the factors based on a scale of 1 to 10. After researching each factor and assigning a score, you are then asked to pay special attention to the factor with the highest score.
The reason for putting the highest ranked factor at the top of the list is to emphasize its importance and prioritize it over the other factors.