Imagine if you and a friend entered a large, empty cafeteria, got your meal, sat down, and started eating. It would be so quiet your voices would echo. Then two more people come in and do the same thing. They start talking and it gets just a little bit more difficult to hear your conversation, so you and your friend start talking louder. Then more and more people come in start talking and the background noise gets louder than the foreground sound until you need to wear earplugs just to hear yourself chew.

That is the state of advertising. If only one player in a market advertised, they might derive some advantage but now people have to pay advertisers to scream the name of their product just because their competition does and no one can even hear the name of the product because everyone is screaming.