Suppose that of the three attributes motivation, initiative, and talent two of them are very much within the control of the employee and the other less so.
The goal of the incentive is to make the employee want to maximize all three rather than doing other things (such as wasting time, etc.).
Imagine the slow, cynical organizations that give everyone a 5% bonus year in and year out no matter what. Just show up, put in your 9 to 5, and collect your bonus.
Bonus/incentive programs are intended to create more of a dynamic. Yes it's more stressful but the idea is that it's worth it.