If we are focusing on developing product features, it will be based on our assumptions and vast user personas and we keep on developing the features before actually releasing a Minimum Viable Product in to the market and evaluating user responses. So, that will take more time for the product to reach into the market and we will get the feedback only after a prolonged time and by then it is of high probability that the competitor products might come up and take advantage of the market demand and conditions.
Instead if we focus on some core basic experience of our target users, and release an MVP and understand their responses, we can improve the product in a better and fast way.
Consider the example of Microsoft Word. Majority of the users may not be using all the features of it rather they will require only few features. Even though MS Word is feature rich, it is not cross-platform friendly. But Google Docs does a wonderful job with regard to that.