On desktop you can change window sizes to what you want. Don’t like wide text? Use part of the screen. But the inverse is not true: if a site decides to stay skinny you can’t make it wide if that’s what you prefer.

This is why I miss square screens. And I miss proper UI/UX design which makes good use of screen real estate.

Not just you. For more than a quarter century, we've known that if a paragraph's text lines sprawl across a wide screen, it's more difficult for most people to read. (And the same is true if the lines are too short. There's an optimal range.)

https://jamesmattison.co.uk/method/why-line-length-matters-for-legibility/

For this reason, it's good for a website's style rules to limit how wide (measured in characters) a column of text can get, regardless of how much screen there is to expand into.

If you don't want to change the window size for whatever reason, I find that reader mode (F9) solves this problem pretty well.