Why does the webpage animation move on scroll? Why is it not just a video? Most trendy product websites do this now (including Apple), but I can't figure out w

Why does the webpage animation move on scroll? Why is it not just a video? Most trendy product websites do this now (including Apple), but I can't figure out why? As a user, it feels extremely laggy since I don't scroll perfectly smoothly. I feel like they would have a better grip on the smoothness of the rendering if it was a simple video? I also don't like it because it feels like I have to scroll "hard" for the page to scroll down. What's the benefit of this? I genuinely would like to know.