According to Sky Sports, the agent for Eduardo Vargas has helped to explain his client's decision to join our next opponent in the Champions League as opposed to making the move to the Bridge. According to Christian Ogalde:
The choice must not be dictated only by economic reasons or the club's coat of arms but also by the possibility to grow and show qualities. The interest of Chelsea? We would have been proud of his move to the Blues and we certainly would have got a higher wage, but Napoli was the best solution for everyone. The club were determined and showed us that they strongly believe in the potential of the boy, who can express his talent in the Azzurri shirt.
It certainly sounds as if Vargas was more concerned about assuring he'd get plenty of playing time rather than immediately joining a top European club, and at this point is his career I can't say that's really a bad decision. As much as I'd have loved to have seen Vargas in our shade of blue, Napoli is certainly a good team in a good league where he'll likely have an easier time ensuring himself plenty of playing time to continue his development. It also potentially makes losing one of their top players over the summer more palatable for Napoli, so I'd expect to see plenty of speculation regarding Hamsik and Cavani in the coming months. Enjoy Napoli Eduardo, just don't do anything fantastic against us.