The cars are more expensive to produce, is probably the best answer I can give.
Overall, though, I think they do it to quickly prey on those people that don't really follow this kinda stuff in the form of a "Whoa, there's a sticker, it has to be legit...Buy it Now!". Before, just making the packaging look 90% identical to the original was good enough to fool people that weren't knowledgeable about these KOs, and now, with the addition of the sticker, it's all the more "authentic" looking.
Now that a lot of people who didn't know anything about these before now do, that novelty has worn off, so they're slapping on price stickers to try to lure some more people in...granted, they're not doing themselves any favors by using these stickers on the existing easy-to-identify-as-KOs items. The next step will probably be finally fixing all the errors on the KO packaging (spelling errors, hole punch placement, rubsign vs. non-rubsign, robot vs. vehicle bubble sorting, etc.), and continuing on with the KO TRU stickers to make them indistinguishable from the legit vintage product.
I mean, seriously, if sites that document these KOs, like HighEndTfs.com, didn't exist, pointing out the (sometimes minute) differences between the KOs and real Transformers, the number of people thinking they've added legit G1 toys to their collection only to have been duped by some sleazeballs would be astronomical. As it is, I'm sure more than a few people have been fooled by these things just because they didn't know where to look on the Internet, or maybe the thought that these toys could be KOs never even crossed their mind.
The KOs do evolve...there are at least three iterations of the Devastator Gift Set KOs that have improved upon the look of the packaging (corrected the format errors, edited the colors, etc.), with each attempt looking more and more like the real deal.
Assclowns.
MIKE
engledogg
