Why Do So Many Modern Websites Use So Much CPU and GPU?

One reason this happens is that teams test on expensive, modern hardware and fast connections. Effects that seem smooth on a developer's laptop can stutter badly on cheaper machines. A good practical test is to use low-end hardware and cut animation first when performance suffers. Most small-business users would rather have a page that loads quickly and keeps their laptop quiet than one with elaborate motion effects.

The problem is real, but it isn't unavoidable. Marketing sites often accumulate huge numbers of scripts from analytics, tag managers, chat widgets, A/B testing, and advertising vendors. It's not unusual to see 100–300 requests on a fairly simple page, especially when nobody owns the job of removing duplicate or obsolete integrations. Many developers are pressured to ship features quickly, so performance gets treated as someone else's problem.

A lot of showcase and portfolio pages are built to make a visual impression rather than to be practical. Full-screen video, WebGL, parallax scrolling, and constant animation can keep the GPU rendering continuously. They may look impressive in a short demo, but they can make ordinary laptops run hot and drain battery quickly.

The examples mentioned are probably intentionally excessive because they're portfolio pieces meant to sell creative work. The company commissioning them may care more about making a statement than saving bandwidth. Regular applications and business websites have stronger financial reasons to optimize, although plenty of web apps are still bloated.