120 on an 11 inch screen might be highly eyesight-dependent, especially if there is anything else on the screen at the same time. Not everyone worth hiring in the industry has optimal vision.
I think 120 might even be pushing the limits of conscientiousness.
There's definitely a bit more flexibility - not infinite - when you only consider the full-scale case. But one is often less productive with that as the only viable option, or else one has external monitors in which case in that usage pattern the laptop is effectively a desktop.
The real fallacy is in denigrating the side-by-side workflow. Just having every window be fullscreen would be madness.
Anyway, one doesn't have to go to that extent to make the point: as per the sibling reply from d_, even on a 17 inch monitor one can have issues with 120-character lines if viewing two files side by side (or 50% browser 50% editor).