Why are Amazon's web pages so cluttered?

UI designers aren't the one's filling the pages up with content. You will find the occasional re-design focused on reducing the clutter that emerges, but the top pages of sites like Yahoo and CNN are driven by different departments competing for space, and trying to justify their claims with user behavior analytics driven by profit. When greed competes, the product is ugly. Zero zen.  When content competes for space, there is conflict between the elements within the page. This results in greater noise and more mixed signals to sort through for any goal a user wishes to accomplish. This is a bad thing. Amazon also fails with layout consistency. Almost every component is a different size, and the spacing is horrible. Amazon also fails with fonts. The fonts used in graphics are all over the board, and in content, they use far too many sizes and colors. Regarding the Greun Transfer: The Greun Transfer is not a graphical solution to an interface problem. Sure maybe they succeed in getting you to stick around. But that has nothing to do with the horrible layout and inconsistencies throughout. Would you rather be lost in a 5 star hotel or in the back alley of WalMart?

A slightly different perspective (I have zero affiliation with Amazon): let's consider brick-and-mortar retail experiences. Those experiences should reflect their respective brands. An Apple Store, for example, is clean and minimalist by design. Products are presented almost as jewels to be admired yet touched, one at a time. This experience reflects the Apple brand.Amazon, on the other hand, is more like an open air bazaar (or cacophonous super store). Many choices, often competing, usually presented right next to (or on top of!) each other. When we go to a large open air bazaar, we expect it to feel bustling, busy, and packed to the gunwales with products on overflowing racks and tables. But there is an order underlying it, an organization, that facilitates the experience of finding and buying things.Imagine if a Tiffany retail store felt like an open air bazaar. It wouldn't make sense. Likewise, imagine if someone tried to redesign the open air bazaar to be more like an Apple store: it wouldn't work, and it wouldn't match our expectations. So while others have pointed out (correctly) that Amazon's experience is tried and true—not to mention well-tested—it's also a reflection of the Amazon brand: The Earth's Biggest Selection. Everything from A to Z (heck, it's in their logo). It's not for everyone, but it works well for Amazon.Everything from A to Z:  

2 easy reasons: 1. Scrolling is easier and faster than clicking. 2. More information helps to make the purchase decision. As for your specific questions, let me just pick one to answer: "Why two columns of customer reviews, one wide and one narrow?" -> The wide ones are the "most useful reviews", Amazon is drawing your eye to them, these are the ones that'll likely be more helpful. The narrow column provides at a glance a sense of what the other reviews say. Remember: scrolling is easier and faster than clicking. It all makes eminently sense, and has been tested to death for years.

I agree with Jason. However, the flaw is the testing only applies to those who visit the site. I don't shop Amazon because it's an experience nightmare. I'm pretty sure I'm not the only person who casts their vote that way. As someone else mentioned, using Amazon (or any UI for that matter) does get easier over time (read: multiple visits). But if you don't return  then you have no "say" in any adjustments going forward. Consequently,  it gets to be a self-fulfilling prophecy. They've built an experience  that serves returning visitors but "excludes" those who do not fit that  profile. And so on and so on...

They simply don't care if we or anybody specific like their design. It has evolved over the years, but was built right from the beginning to work on even the oldest browser and ugliest phone. And millions of users are now used to how it works. It isn't easy to transition such a massive user base to something new, especially if design isn't an issue for them anyway. So Amazon takes the path of slow and small changes, every now and then. You can barely tell it is changing. But that's exactly the point. They don't want a shitstorm of angry users :).

Amazon is famous for its A/B-test-driven-design. If that is really the case the team is focused on optimizing page performance (conversions). Makes sense for Amazon as that is what drives value, not visual appeal.

Their UI design is time-proven. You get lost in the amount of information and are constantly enticed to check-out other, similar or related products, learning about products you never heard thus making you buy more. It's similar to walking into a cluttered store with many things to explore and having a group of interested people giving their valued opinions about everything you see. The store might be a nightmare in terms of design, but you get lost within it and suddenly find yourself with a bunch of products in your shopping bag that you never intended to buy in the first place. Welcome to Amazon!

Because it's using the Gruen Transfer. The gruen transfer is a design term for when designers design things, for the intentional purpose of making you lost. Amazon is one of those websites that wants you to get lost on their site. I've always wondered this question myself, and why they can't design their site in an organised and predictable manner. Learning about the gruen transfer, I then found out the answer. I've always wondered why the product pages on Amazon were so long. I realised that this was because they wanted you to get lost on their site, therefore you're discovering new things to buy, of which you wouldn't have, if everything was neat. Of all the shopping websites, shopping on Amazon is most comparable to shopping on the high street, because you can never know where you'll go, and what you'll discover along the way. I used to think that Amazon's design was stupid, but when I learnt about the gruben transfer, I realised just how clever it is. By having panels such as Listmania, Customers also brought, Frequently Brought Together, it provides an unrivalled experience that no other online retailer has been able to replicate. There's a reason why people love the shopping experience on Amazon, though they don't like the design, and this is why. Supermarkets and Facebook also use the gruen transfer, but let's not change the subject.

It has an extremely high information density, which is useful for people who are familiar with the interface.  You assume that because they could entice people to buy more items if the interface looked better.  I'm not sure.