Because it works! Google tried to penalize these sites with popups by reducing their SEO rank. Yet, they found workarounds (like 5 second delay) to show these p

Because it works! Google tried to penalize these sites with popups by reducing their SEO rank. Yet, they found workarounds (like 5 second delay) to show these popups. The point is - they are not "low skill" marketers. They do it, because the signup conversions are usually 4x higher than not having the popup. Popups force users to make a choice. Users who are not interested in the site will be annoyed and leave the site. Users who are interested will signup, if you offer them something more (like discounts). So, while you may not like it, it does the job!