Because some of its training data included some of the many, many websites out there that describe marketing techniques. However, your example has actually proved my point - the red sports car is a car for insecure middle-aged men needing a mid-life crisis penis extension. The LLM has entirely missed that cultural association, and has basically suggested a red sports car for a young audience, when an alternate colour would actually be more appropriate - because it doesn't actually understand what a red sports car means.

It also hasn't actually picked any distinctive elements that couldn't be found on a website offering generic marketing advice. "A dynamic composition" is obvious, but it hasn't specified any details about what the composition should look like. It hasn't detailed any of the surrounding scenery. It says you should include a brand name logo, which was obvious because you prompted it to come up with a brand name, but it's failed to detail what those should actually look like. The entirety of the elements it's created here is "sleek red sports car", which has a cultural connotation inappropriate to the target audience, and the rest you could literally get from any search for "how do I create an advert for a car?"