The concept is called "Banner Blindness".
Users have learned to ignore content that resembles ads, is close to ads, or appears in locations traditionally dedicated to ads.
Basically, we have developed an instinct to automatically ignore anything that looks like ads. They can appear in the page, right in front of us, but they don't register in our brain. Same reason we automatically close promotional pop-ups or just blank out commercials, etc.
The more companies want to push promotions with big flashy annoying and obnoxious implementations, the more likely they will be ignored. We hate ads so much we call them internet cancer because the web would be un-browsable without ad blockers.
The best way to handle important information is presenting it in a readable and engaging format, making sure it's findable, it's concise and to the point and addresses exactly what the user is looking for (no marketing filler fluff). Make sure it's understandable in layman terms (e.g. most return policy pages need to be re-written in layman terms, picture an already frustrated customer trying to understand legal jargon).
Think about cooking recipe blogs and how people complain the recipe is often 10% of the content and all the way in the bottom. It's a reaction to marketing fluff and unsolicited content: People arrive from Google for the recipe, not to learn about the author's entire life story. The engaging part happens in the recipe content itself. For example, steps are clear and concise, understandable, supported by short visual clips of how to do them, special ingredients have replacement alternatives or links to buy them, the recipe is formatted well for printing for those who like using paper, etc.