"Banner Blindness"
According to Nielsen Norman Group (2018), the term "banner blindness" refers to the selective blindness people apply when viewing a website.
In other words, the brain can ignore any information that is not relevant.
People's attention span is limited, so they only focus their attention on what is relevant to the task they are performing on the website, such as navigation bars.
By looking selectively, they ignore all content that visually resembles an advertisement, or that is located in the area where ads usually appear - since this content is perceived by the brain (correctly or incorrectly) as advertisements -.
This is due to the Gestalt Law of Proximity, which explains that elements close to each other are perceived as related and will form part of the same group of elements.
To track and prevent this from happening, usability tests can be performed. Ideally, test a group of users and conduct an eye-tracking study to determine which the "hot" areas are, where users are focusing their gaze, and which the areas where they look less are, or simply ignore the content completely.