Because you can

When you decide to take the more difficult path to do things that truly matter, a common thinking pattern says that if you do this, in the end you will be rewarded. Then naturally people choose to do projects that have a reward associated with it (get this, achieve that).

When rewards can be measured, the importance of the project can be judged from looking at the reward. The greater the reward, the more important the project is. 

The problem with this thinking is that some rewards are difficult to measure (compare the number of people who attended your recital with a tear in an elderly woman's eye afterwards). If the reward is difficult to measure, many people tend to stay away from such a project.

Another alternative is choosing to do things that matter simply because it's the right thing to do. Because you can.