People often need motivation to do tasks they'd prefer not to do. Do you work? Your motivation is your paycheck. Lost something? Finding it may provide motivation to tidy the house.
At the root of the word motivation is the word motive, which is similarly defined as the reason for a particular action. Although the words are synonyms, when it comes to criminal behavior, people generally ask about the motives leading to the criminal acts, not the motivation behind them. Other synonyms for motivation include inspiration and enthusiasm, so people tend to associate motivation with positive acts.