Due to night-time driving, all car models had to be upgraded for both lights and interior dashboards illumination.
I guess it took some hefty time to get it right (lights colors, illumination colors, etc.), so the probable reason is partially because of that.
You'd think they would model all that stuff in the first place to save them having to go back to certain cars, especially rare ones. I know that the Mitsubishi Starion they laser scanned for Forza 4 had it's headlight functions done(the owner said so), even though they obviously didn't use the headlights in the game.