Jeff Bezos knows exactly what he is doing. Amazon is, at its core, an infrastructure company, much like your plumbing or your electricity, except it's one level above those. It's major offerings are infrastructure for web services, infrastructure for shopping fulfillment, infrastructure for digital publishing, and probably a few others. Sure, it is willing to make money by using its own infrastructure to sell you books, shoes, and industrial supplies. In fact, it built the infrastructure to do that, but even if the lion's share of Amazon's profits right now come from selling over the web to consumers, it is not the business that Amazon wants to be in.
Amazon wants you to build a business on top of Amazon where you do the marketing and decide what to sell, but use Amazon's Web Services, Fulfillment, Payments and Digital Delivery to run it.
This is the reason bezos thinks long term. because he can.
Some of those parts are:customer trust,the need for computing,fulfillment,delivery,payments and access to targeted eyeballs,all content will be digital, need for marketers(affiliates).
Serving as a leading infrastructure platform is a great way to achieve this.It gives you revenues , it puts you under customer pressure and i think the new market dynamics works better for amazon also as an integrated retailer, by letting amazon control prices and service levels and limiting the platform, by decreasing competition to a small number of companies in the industry and by pulling startups towards them.
Now combine the (small?)benefit of each platform gives you over competitors, together, and you got a big competitive advantage.
On the other hand, having a great platform let's you profit and learn from the things that change fast.