Just imagine having an outlet without having any signage onto it – no name, no windows…nothing in particular. You would expect people may drop in out of curiosity, looking for product A, whereas you are selling product B. Now, when you have a shop with a proper name and probably the product image on it, this would attract so many people off the street, and they would ask for what you sell, and some of these customers would tell other potential targets about their buying experience and about your products and your shops.
SEO is not only about search engines but good SEO practices improve the user experience and usability of a web site. Users trust search engines and having a presence in the top positions for the keywords the user is searching, increases the web site's trust. SEO is good for the social promotion of your web site.