[oneeyedpigeon]

It's a fair point, but it's hardly unique to Jupyter. In fact, while 99% of websites suffer from this problem, I think it's unfair to highlight it specifically wrt Jupyter. Heck, even the site we're on right now does a poor combination of uncomfortably-long lines AND unused left and right margins.

[ZitchDog]

99% of websites are not insanely popular development environments. vscode.dev, for example, takes up the full browser width.