80 characters is way, way too short. I think 120 is a decent spot for today's displays, although I don't mind even longer than that either.
You want to be able to do side-by-side diffs on your laptop using a normal sized (not tiny) font.
You want to be able to paste snippets into design documents and emails and blogs without accidental wrapping or truncating or scrolling.
80 is nicely legible. It works really well.
Going from 80 to 120 will net you, what -- an extra 2 or 4 lines in your viewport?
It's not worth the optimization when you lose so much for the reasons I described.
I also tend to work on a single file at a time versus trying to view multiple files side by side. But when I do want to do that, I'm not trying to work on a laptop monitor, so I have 2 monitors for that use case.
The white space I have available but typically don't use, simply doesn't bother me. I like some white space, I'm not seeking out density as some productivity hack, I can tab to another file when I want to see it, seeing them both at same time isn't a huge requirement of mine.
It sounds like you have a job that has you frequently doing code jams on a tiny monitor (why? you got pulled into someone's office? you coding on a train?) so this works for your normal situations. You're not understanding that I avoid those situations. I code from a desk with a full setup or I don't code, I take notes about what changes need to be done when I get back to coding.
Long lines are less readable and I want to have several terminal panes or editor windows side by side.
Some languages are just naturally worse at this (eg. Java), so there is always some flexibility. But for most languages that don't have multiple levels of indentation by default and the custom of overly long names, 120 is more than enough to be a good guidepost.
When I'm coding for myself, I use all of that at times. I love that there are some things I no longer have to break onto multiple lines any longer.
Also, if you have a ton of nested loops etc, then you don't end up with that problem where you can only see the first few characters of the deepest lines.
Also, excessive nesting is almost always a code smell.