There are many factors that could make an individual a target for human traffickers, such as:
Those people who live in extreme poverty, need money right away, and tend to find a way out in dangerous rather criminal businesses.
The ones who are trying to pursue his/her dreams (such as becoming a famous top model or a soccer player) end up in schemes and tend to be easy targets for human trafficking.
Also, some people might feel lonely and the solitude makes them go after a more meaningful or risky solution to their problems to make them feel alive and end up in the hands of human traffickers.