The Impalas are cheaper, and may not be so much that they "stick" with them but have a set purchase contract with an ongoing delivery schedule.
IIRC, the NYPD is the single biggest purchaser of the Impalas, it's possible GM/Chevy extended their production life to fulfill an ongoing purchase contract, as it is they reduced the 2014 exterior color choices to just 4 colors.
IIRC, the NYPD is the single biggest purchaser of the Impalas, it's possible GM/Chevy extended their production life to fulfill an ongoing purchase contract, as it is they reduced the 2014 exterior color choices to just 4 colors.