Lots of theories out there. The one is for sure, it’s not only about money. Because in the end money is a tool to make or get something that really matters. If you want to build a house it is The house that you want, or even further, The comfort that you will get in this new house built according to your dreams etc.
But when we talk about money as a compensation for a job it is often the same. If you consider a certain salary at an expected level of what you can make, this will not motivate you nor demotivate you. If salary is below expectations it will demotivate. If salary is above expectations it will motivate for a short time, then it will become a new level of expectations and so will neither motivate nor demotivate you.
So what motivates people?
I believe there are three things that motivate the most: achievement, freedom of decisions and responsibility.
While achievement and freedom of decisions may seem kind of obvious, responsibility often stays at the opposite side, being often perceived as something people do not want. While it is sometimes true, this is an essential part to let the freedom of decisions to be taken seriously. Because when you have a responsibility, that means that the game is serious now and all decisions are “real” and may lead in both good and bad directions. So when you eventually succeed, you have much more satisfaction from the taken decision just because there was that part of responsibility.
The same way achievement builds up on responsibility. Responsibility makes you feel the ownership of the achievement, that it was not accidental but it was a conscious set of choices you made because you felt responsible for some direction or area of development. So the “true achievement” via responsibility and risk of failure.
One more thing to name and it is often not being mentioned due to the lack of some gravity, it is fun as a part of motivation and happiness. When things bring you fun you keep your motivation longer because you enjoy the ride. And this is super important. As we are in the continuous state of pursuing our goals, it would be a waste of life not to enjoy the process.