My view is that there are two primary motivations:

1. Money
   • As a contractor providing services which are in demand you can charge a premium rate
   • If the demand for your services offers continuity of work, you can realize significant income well above what you might have earned as a employee.
2. Security
   • Many people have worked for years as employees, believing this loyalty would create job security, only to see their jobs disappear as the result of common business strategies such as: mergers, Acquisitions, Outsourcing, Off shoring, etc.
   • Unless you work for  some level of civil services the idea of a job for life is a myth and even then, it can be at risk.
   • As a contractor you can provide specialized services and through experience and training can position your expertise so that it appeals to the client community and ensures work continuity.
   • Your skills and experience are what ensure your security.