There are a number of reasons why this happens, but one of the most common is that companies simply don't have a clear understanding of their target market. They may create a product that they think is great, but if there's no demand for it then it's not going to be successful. This is why market research is so important. Companies need to understand who their target market is and what needs or wants they have before they can create a product that will appeal to them. Otherwise, they're just shooting in the dark.