There is little reason to when you can walk into a supermarket or department store, often with three or five of them within 1000 feet, and buy what you need at the normal marked price. If you cannot go there yourself, most of them offer home delivery anyway. You also know who you are buying from, you do not have to worry about questionable third-party sellers, and if there is a problem you can telephone a human being or simply walk back into the shop. What is not to like?
But yeah, not every city or country is lucky enough to have such a strong retail network. Amazon makes sense in many parts of the world. But I also think its success in those places is a sad indicator of weak local infra and underinvestment in local retail.
The world would probably be an economically healthier place if every town and region could support a strong network of supermarkets, department stores, and indie shops. It keeps more money circulating locally, supports more local jobs and improves local economy instead of funnelling all the money through one gigantic company.