And now you've got me curious; who does want this? Is it just designers who really want a very specific experience, down to the way things move onto the screen?
Yep, I worked as a front-end dev since forever and I can confirm that I've been routinely asked by designers and other product people to
- Change how scrolling works, incl. arbitrary scrolling angles and non-linear scrolling speed
- Change how the fonts (and SVGs) are rasterized by the browser
- Disable browser features, such as zoom and back button
- Take over the browser's UI in other disgusting ways
...I work as a backend dev now, it's a happy place where people genuinely care that the SQL query runs fast, but nobody ever asked in which font it renders in Firefox on macOS.
My guess is that it originates with designers who build these web pages as basically Keynote / PowerPoint presentations.
It’s shown to management, everybody oohs and aahs at the clever transitions between slides… And then the developer is stuck trying to replicate that “unique experience” with the designer breathing down their neck.