According to Chapter 17, why do people choose the path of Preya even though Shreya is the better choice, and what is the true purpose of human life?

Chapter 17 explains that although the choice between Shreya and Preya is within a person's control, making the right one is difficult. A dull-witted person is conquered by Preya because they lack discrimination and detachment. As long as the senses crave worldly objects and there is an obsession with things like gold and women, Preya remains sweet and appealing. The chapter states that the true purpose of human life, or Purushartha, is to discard the pleasant path of Preya and honor the good path of Shreya. This requires firm human effort, akin to the swan that takes only the milk when it is mixed with water.