If the behavior of people who are in the profession of making money isn't well explained by the motivation of making money, then it seems a real stretch to apply it elsewhere--for example, to nurses.
If the behavior of moneymakers isn't well explained by the motivation of making money, it seems difficult to apply it elsewhere. 
If the behavior of people who are in the profession of making money isn't well explained by the motivation of making money, it is easy to apply it else where, such as to nurses. 