"Too much information" in ads = too much lost
Who doesn't like to get more for their money? It gives us a sense of accomplishment... that we've gotten a bargain.
However, more for our advertsing dollar can actually mean less. More words and images in the ad means that readers might actually see less due to all the clutter.
Look at these two ads from a local newspaper. The layouts of both ads have so much that little can be seen. Words and images get lost in all the information. And lost information mean less effective ads.