Before the invention of the printing press, there was no way to replicate materials that was anywhere near as cheap, quick, and consistent. A drawing, a line of text, a book, a sign- all of these had to be made and replicated by hand. Understandably, replication was reserved for whatever a culture deemed most important, and replications w ere often restricted to the wealthy. The invention of the printing press allowed a leveling of the playing field- multiples were no longer limited to the wealthy and the important. It allowed the ad-saturated world we see today to develop.
Advertising existed before the printing press, but in a much more limited capacity. Town criers, papyrus leaflets, and paintings on buildings are all forms of advertising that were used before the advent of the printing press. Obviously, these were incredibly localized and specific forms of advertising. However, the printing press eventually allowed companies to expand their advertising and their brand. As printing became easier and prices went down, even smaller companies could afford to plaster their name all over town. Now companies needed to put effort into designing an image that would be eye catching and able to be produced with the technology available, and the world of advertising that we love to hate was born around this need.
Of course, early printing was still more expensive and time consuming than it is today. So advertisers naturally tried to exploit their limited space as much as possible. The cramped, word-heavy style of early pamphlets and flyers can be seen below.
Slowly, advertising and printing have evolved to the point that you can see a host of joke flyers pasted on Baltimore stop signs- print is cheap enough that almost anyone can have their own anonymous laugh displayed all over the city. Whether this is a good thing or not- well, that depends on who you ask.