Before the Macintosh made graphic design accessible to everyone, it took a lot of trouble to create an ugly flyer. Now everyone can make ugly flyers. They might start off doing dorky stuff, but the ones with an interest soon begin looking around to find out how to make it better. Now every small business creates their own newsletter, and businesses that never would have spent the money to hire an ad agency have created their own. And since advertising is less expensive when you do it yourself, businesses create even more of it.
Corporations have numerous in-house departments that design and produce their own work.