Kings have Ben McLemore and Marcus Thornton at SG already. Plus, they play a fair bit with two PGs since Vasquez (6-6, 215lbs) has such great size.
Lack of available minutes. No real need for a Courtney Lee.
Maybe if they wanted to dump Marcus Thornton. Say C-Lee + filler for M.Thornton. Boston to take on some extra payroll this year and next to get out of Lee's third remaining year. Kings get a more defensive minded guard to complement their other more offensive minded guards (Isiah, Vasques, McLemore). A more low usage guard who will complement them better than M.Thornon does.