Because you want to sit there doing nothing until suddenly something from outside strikes you and fills you with energy, motivation, ambition, and desire and makes you want to go do it without you doing anything but sitting there. We call it waiting for a miracle. It is not the best plan for life. You don't wait for a miracle. You must make the miracle.
Most people say motivation but the good news is that the answer is action.
Now, you are back to waiting on a miracle. The secret is to act first and allow the motivation will follow. This actually happens to us all the time. For example, just recall when you were asked to go somewhere you did not want to go. Maybe it was to the ballet, family reunion, or mud-wrestling match.