In my experience, people who use wide monitors are more OK to longer lines. The opposite is true for tall/vertical monitor users. The next question: What is the chicken and what is the egg? Do people prefer narrower lines because they prefer tall monitors? Or vice versa?

All of my main external displays are 27". The diffs fit perfectly on them with the 80 character limit

You must have your text size set to 18pt or something, because I can easily fit 3-4 columns of 80-char text on my 27" monitors.

It's whatever the default scaling is on GitHub. I could fit more in other contexts of course, but on the site, that's the perfect size with a 27" monitor