I don't doubt that the material is useful. What I really don't understand is why it's all plastered with brands. I'm guessing since I don't recognize the brands they're cycling brands. I guess it could be explained by jfer_rose's comment that "people are convinced that every new activity requires stuff." I live in the 8th most populous city in the US, though, so I don't think it's changing strictly based on big cities.
Alright, I feel like you're asking two different questions, which I suppose explains the misunderstanding above. As to why cycling clothes are often covered in branding, there are a few reasons that I see:
-People wear protour jerseys on casual rides like they wear baseball jerseys to baseball games. It's a way to support your team, feel more involved, or whatever. I don't do it so I don't know all of those people's motivations, but they're similar to any sport.
-A surprising number of people actually are on racing teams with unique team kits. They're not "sponsored" in that they're professional, but their team probably gets some money to do cool things a couple of times a year. These people represent the majority of the NASCAR-style kits that have 10-15 sponsors per uniform.
-Middle-of-the-road cycling clothing often has a huge logo representing the clothing brand. Cheap clothes and very expensive clothes usually don't do this. Again, I don't wear these so I don't know all the motivations, but they may include showing pride in a relatively expensive purchase, liking the looks of the logo (some are very stylish), or maybe even deciding that the logo was tolerable in exchange for more comfortable clothes even if they don't like the look.
I don't think "people are convinced that every new activity requires stuff" explains the prominence of corporate logos on cycling gear. That seems more to me like a somewhat pessimistic anti-consumerist answer to the question of "why do people wear cycling clothing", which is what I thought you were asking before.
Kriegsspiel, most of my German friends drive. There may be self-selection in the Germans who come to the US, but they bike at a far lower rate than other Europeans in the US.
All of my German friends in the US ride bikes, while few of my other European friends who live here do (and I'm not just making this up to fuck with you). I don't believe this is the sort of thing you can make sweeping generalizations about with nothing more than a few anecdotes.