That's just because capitalism as taught in college micro/macro classes assumes a perfect market with no differentiation and lowest price always wins. But in reality it costs money to disseminate information (marketing) and deals are not struck in a perfect market. And differentiation is not only common but desired by sellers.

I'd also add that government tends to magnify these distortions since it gates access to a lot of demand behind a bidding process that's heavily politicized and reliant on lobbying. So the market as thought of in economics doesn't really exist anymore.