Term and Condition

Mark PaperMaster is supposes to join APPLE as iPod chief developer. But due to the term and Condition that restrict by previous owner IBM. He has to cease work and involve himself in this court case. According to the agreement with IBM, he cannot join competitor if he leave the company within a year. Why is such T&C apply on so many different field of job? If a soccer player not able to join competitor within a year of leaving his club? I think a lot of player already sat at home a long time.