They go over how the web and frameworks decided against horizontal, apart from deliberate emphasis, they go over some desktop layout attempts, failures and successes (more of the same vs navigation), a chapter about (paper) documents as the source, and endless panes now using horizontal.

From the description:

Almost every screen we use is a landscape rectangle, wider than it is tall. And on almost all of them, the content moves vertically. Always down.

This video walks through a wrong question. If mobile scrolls down, why doesn't the desktop scroll sideways?

The question turns out to be wrong.

Chapters

• [00:00] Introduction
• [01:23] The Web Could, and Doesn't
• [03:18] The Microsoft Bet - Windows 8 "Metro"/"Modern" failure
• [06:18] What Makes a Difference - Layouts where horizontal works
• [09:14] Horizontal Scrolling as Emphasis
• [10:24] When Horizontal Axis Means Something
• [12:13] The Document Model
• [14:06] The Potential of a Glass Plane

References

• Tim Berners-Lee, Information Management: A Proposal, CERN, March 1989 : http://w3.org/History/1989/proposal.html
• Tim Berners-Lee, HTML Tags, late 1991: http://w3.org/History/19921103-hypert...
• Jeremy Keith, A Brief History of Markup, A List Apart, 4 May 2010: http://alistapart.com/article/a-brief...
• MDN Web Docs, overflow: http://developer.mozilla.org/en-US/do...
• Chen Hui Jing, The horizontal overflow problem: http://chenhuijing.com/blog/the-horiz...
• Beware Horizontal Scrolling and Mimicking Swipe on Desktop: https://www.nngroup.com/articles/hori...
• Responsive Web Design: https://alistapart.com/article/respon...
• Building Windows 8: • Building Windows 8
• Niri Wayland Compositor: https://github.com/niri-wm/niri
• macOS Spaces: https://support.apple.com/en-gb/guide...
• Myspace shows off redesign, promises invites soon https://www.nbcnews.com/tech/tech-new...

Mousewheel. End of study.

Tldw? (Any video is Tldw)

This would be my guess. Fingers can wiggle up and down easier than side to side. /shrug

It's also how we're trained for thousands of hours to read text. Left to right, then progress top to bottom. That makes more intuitive sense to more people than scrolling endlessly to the right.

the web is not vertical because the spec demands it, the web is vertical because the people who design websites the people who write the frameworks and the people who teach usability all agreed implicitly and over 20 years that sideways was a layout failure

I forgot to add the description and chapters. I added them now.

They go over how the web and frameworks decided against horizontal, apart from deliberate emphasis, they go over some desktop layout attempts, failures and successes (more of the same vs navigation), a chapter about (paper) documents as the source, and endless panes now using horizontal.