That's a pretty unhelpful way of thinking about this.

Any web designer who doesn't, in 2021, understand and make allowances for 4k/5k ultra wide monitors as well as phone sizes screens in portrait mode - isn't doing their job right.

The problem here is not the monitor shape or the user's browser window width, it's the css (and maybe html) and the lack of understanding of how to use it properly (or, more sympathetically, perhaps a conscious choice on the part of the people paying for the website to not allocate enough budget to cover all their competent webdev's suggestion?)

The designer here did make allowances for "ultrawide" monitors. He stopped the lines of text becoming unreadable by wrapping them at something reasonable.

There are precious few reasons to run a web browser full screen on an ultrawide. Most web sites don't even go that wide, it's just a ton of wasted screen real estate.

I wonder what % of users:

1. Have an ultra wide monitor.

2. Regularly use their browser in full width mode on it.

Pretty much everyone I know with an ultra wide snaps their browser to the left or right side - having a single browser window that wide is not very useful, and makes lots of websites look weird.

I’m inclined to agree. Even on a normal sized monitor I almost never fullscreen my browser.

Yes, I want an entire paragraph on a single line. If I wanted the content to be narrower then I'd make my browser narrower.

http://motherfuckingwebsite.com/ looks great on an ultrawide. It's pathetic that so many websites don't.