It was primarily because skeuomorphic UIs don't scale well with user experience levels. They're easier for novices but don't lend themselves well to expert use, unless you add a bunch of extra affordances that would seem really out of place in a UI meant to look like a real thing. And what does a skeuomorphic web browser or email app look ike? We don't have those in meatspace.

It was less of flat vs. skeuomorphic than dead vs. alive elements (https://vimeo.com/64895205).

While the technology to create 'alive' skeuomorphic elements now exists, that wasn't the case a few years ago.

Older skeuomorphic designs were static/rasters which were clunky to either mix these static elements with animated elements (for example the iOS 7 menu title transitions) or to have transparency (how can you have transparent leather/velvet?).

Liquid Glass is actually an extension of the foundation laid by iOS 7.

Many parts of the iOS 7 transition guide might as well have been written for Liquid Glass:

- "Make sure that app content is discernible through translucent UI elements—such as bars and keyboards—and the transparent status bar"

- "Examine your app for hard-coded UI values—such as sizes and positions—and replace them with those you derive dynamically from system-provided values."

https://developer.apple.com/library/archive/documentation/Us...

Not gonna lie, I've been using (and programming) GUIs since the Amiga and even I get thrown askew by "click here to enter your name" (expecting a subsequent GUI element to focus, or worse - a popup) vs. "click here to enter your name" (haha! the prompt text disappears now and this is just where you write it I guess!).

You'd think this is just a little thing, but it can really mess with you if you need to change focus and - of course - every application will 'haha!' you in a different way.

It has nothing to do with skeuomorphism really, but at least skeuomorphism seemed to give everyone an idea of what they were shooting for at least.