Because I said so !!!
But seriously, when these kits were out in stores the anti tobacco and anti alcohol lobby was starting to take notice of of these kits and making noise about how these would get children to experiment with smokes and booze. What they didn't take into consideration was that the people who were buying these kits were mostly adults, and not children that they were trying to protect. The big three kit makers, Revell - Monogram, AMT / Ertel and Tamyia started to remove the offending decal sheets from their kits, and make them more ( I hate these words ) " Politicly Correct ". This is why I think that they should be regarded as collectables. The only way now to build a tobacco sponsored car is to purchase them from an aftermarket suppler such as Tabu or Studio27.
Sorry for the rambling history lesson.