Almost all business applications have horizontal menus and ribbons that take up a decent percentage of a landscape monitor instead of utilising the “spare” screen space on the left or right, and a taskbar usually sits at the bottom or top of the screen eating up even more space (yes I know this can be changed but it’s not the default).
Documents are traditionally printed/read in portrait which is reflected on digital documents.
Programmers often rotate their screens to be portrait in order to see more of the code.
Most web pages rarely seem to make use of horizontal real estate, and scrolling is almost universally vertical. Even phones are utilised in portrait for the vast majority of time, and many web pages are designed for mobile first.
Beyond media consumption and production, it feels like the most commonly used workplace productivity apps are less useful in landscape mode. So why aren’t more office-based computer screens giant squares instead of horizontal rectangles?
I tried for a while to use two 16:9 vertically. Like you say, vertical makes a lot of sense and it works great. But web devs seem universally to assume that if it’s a tall narrow screen, to show the mobile version.
Web Devs are also highly allergic to using the 25% of the screen on both the right and left so only the middle 50% is useful space. It’s god damned infuriating!