One of the main triggers is a failure to meet expectations. When a person follows a profile, they want to experience certain emotions or gain knowledge. A shift from expert advice to excessive personal chaos or sudden aggression in the comments forces followers to look for an alternative. In addition to internal reasons, there are technical aspects worth reading about here https://recently-followed.com/why-people-unfo...instagram/ this will help you understand which actions are perceived by the audience as spam or insincerity.
Another factor is visual fatigue and monotony. Even a perfect profile grid can become boring if nothing new appears in it for years. The modern viewer seeks dynamism and authenticity. People unfollow those with whom they can no longer identify, preferring lively and honest profiles.
Eventually, it’s worth paying attention to users’ own “cleanup” efforts. Many are reviewing their follow lists, deleting accounts they haven’t interacted with in a long time. So, focusing on engagement not just on providing information - is the key to maintaining a stable follower count.