Because, in most cases, it wouldn't work. Most pages using scroll-jacking create and/or show certain layers upon scroll. The content isn't there before. There

Because, in most cases, it wouldn't work. Most pages using scroll-jacking create and/or show certain layers upon scroll. The content isn't there before. There are some, like I believe most Apple product pages, where scroll-jacking is used to create a one-slide-at-a-time-effect where it may work. But even on those, individual slides often undergo transformations upon scroll revealing information you'd otherwise not see.