This is completely false. Amazon provides significantly less discoverability than a retailer. With a retailer, you get a product that actually shows up in front of people's eyeballs, and the ability to provide in-store promotions to attract customers, and, most crucially, the store lets you know how the promotions perform. A small minority of retailers make you pay for this data, but most don't because they want products to sell through. Many stores will even work with new brands to promote their products, such as (temporary) eye-level product placement, end-of-aisle placement, special displays, etc.

Source: Before going in-house I used to rep manufacturers of all sizes from startups to billion-dollar behemoths selling to major, regional, and local retail chains. Grocery stores are the best at working with brands (but also the fastest to drop products that don't sell), Target is about average, and Walmart was the worst at the time though I hear they've gotten better.