You watch it, and Google Ads records a veeery long "user is present on website" time, which is a boost in SEO - Google ranks how long people spend on a website, hence the "trend" of endless waffling around in stuff as basic as cooking recipes, or inline videos that entice the user to spend time on the website. Even if all of it (nowadays including videos) is AI-generated slop. But if the user immediately finds the information and goes back or closes the tab, then the site will get punished for being actually efficient and useful.

SEO has ruined the Internet.

Putting autoplaying videos on every page farms their view count and gets the algorithm to show it to more people, which drives ad revenue. It's quite similar to how Fextralife embeds twitch streams to farm viewer counts.