Taking Advantage of Outdoor Advertising

As I have taken public transportation almost every day since I have been in Madrid, taking notice of my surroundings and looking for similarities and differences between the countries I have visited, I have noticed a big difference in outdoor advertising when comparing European and African countries to the US.
In the United States, every open space is plastered with advertisements, whether they are on taxi cabs, buses, random posters, billboard ads, vacant walls, full subway cars, and more. It is impossible to escape advertisements in urban areas.

In Spain, I have noticed that there is much less outdoor advertising. Although it is certainly prevalent, Spain has yet to take advantage of covering every visible surface with announcements and commercials. Here, in the subway system, most of the large poster advertisements are for the subway itself; for example, the multiple life-sized Carmen Herrera posters that adorn each waiting area. In the United States, you are more likely to see ads for television shows and new movies, or even store openings in most of the metro areas.
Take Sol versus Times Square, for example:

Sol is clearly one of the most populated areas in Madrid, yet when looking around the square, one notices the Tio Pepe sign of course, and usually a very large American film advertisement on the square front of the building across from the Puerto del Sol, and maybe another large H&M image as well. It is not plastered with advertisements, nor is it overwhelming to look at. Driving around the outer city parts, there are also many billboard advertisements, but less and less as one reaches the countryside. Even in the most remote areas of the US, billboards creep out from the tree lines and from large fields. A US extreme is Times Square, where there is nowhere one can look without being overwhelmed with neon signs, large video screens, and billboards that advertise new clothing lines, Broadway plays, and movies. Even in smaller cities such as Boston or Providence, each bus and taxi cab has plastered signs all over each side of the vehicle. Just to add another view to the mix, I visited Morocco this past weekend and took notice of the way that they advertise as well. Most of the ads I saw were for Coca-Cola (this product is everywhere in Morocco) and maybe a couple for McDonalds, but honestly there wasn’t much else. They tend to utilize empty building walls to paint on ads, instead of billboards or signs and posters.

Getting back on track, the real question is: has Spain considered these outdoor advertising opportunities and just has yet to take advantage of them, or is it just that the United States is more obsessed with consumerism and capitalism that any manner in which to sell products must be utilized?