Since the dawn of civilization, humankind has primarily used two methods of motivation: threats and bribes, or if you prefer, fear and money. Both are so incredibly effective because they leverage a person's need for survival and comfort. From the Egyptian Empire to our current technological revolution, the tried, tested and true methods still reign to this day. They're still here because they work. Fear and money are two of the most powerful forces when it comes to getting people to do what we want them to and as long as we live in a society where the mighty dollar rules, money shall remain a dominant motivator.
An extreme example of fear motivation is an armed robber mugging you for your wallet. You need to survive. He needs your money. A match made in heaven. Instant motivation. Instant results. Violence and physical dominance is a heck of a way to get things done. With regards to everyday life, can we honestly say that fear doesn't exist in the workplace? That employees don't feel some form of threat on a daily basis? "Do your job or else..." is either heard or felt and as long as the employee lacks a sense of security, it works like a charm.
As for bribes, well, that one is indeed all around us. What is a job after all? It's where you trade in hours of your life for money. We then use this money to pay for things that allow us to sustain a certain level of comfort and perhaps some luxury. The system is dependant on our yearning for this comfort. Now it's not the company's fault the entire world works on this system. It works, and it's way better than global slavery. However, offering money to have someone do something they don't honestly want to do is essentially the definition of a bribe.