If you leverage your business, and data obtained for other reasons, to unfairly depress competition, the end user loses out, and is part of why antitrust legislation exists.

Another example is what Amazon were accused of - using their internal data from providing seller services to then decide which products to launch in their Amazon Basics range - to the point where it makes those other products no longer profitable to sell, and an option for consumers is removed.

If they conducted research without using that data about what products people would like, that's different - that's competing vigorously and fairly.