Haha. No actually most writing needs an editing pass or two before it's "good" and that usually consists of removing unnecessary words and rephrasing to make it simpler. For a wide audience a 4th grade level is often used as a standard. Yes it's because some people are dumb and have short attention spans, but also because there are often things competing for their attention in the context they're reading them. Flyers posted on the street? Yes, lots of things competing for attention. They might only have a second as they walk by, and less words is going to stand out better to grab their attention as well due to the greater white space on the paper and bigger text if this campaign doesn't have a standard text size. Also these are meant to be jarring enough to stick in their head and a shorter, simpler phrase is more likely to do that word for word. But honestly, even if it was just because idiots have 5 second attention spans, we're not doing this to make them smarter, we're doing it to change their feelings around the message, so you do what works.