This isn't completely true. What you're talking about are called "echo chambers" or "filter bubbles", and there are ways to make sure they don't negatively impact users.

Additionally, studies have found that (when A/B testing recommender system vs no recommender system) users create their own, more localized "echo chambers" in absence of a recommender. This is measured by the "diversity" of content consumed, which decreases if a user is their own recommender.