Pop-under ads still exist because they are effective. They allow advertisers to reach users without interrupting their browsing experience. You can see the ad only when you close or minimize the current page. This makes the ad less intrusive compared to pop-ups. Many website owners prefer pop-unders because they have a higher chance of being noticed. Pop-under ads can also generate more revenue as they are viewed for longer periods. Advertisers like them because they can capture user attention without being too disruptive. These factors make pop-under ads continue to be a popular choice in online advertising.