Because you picked that metric.

Of course well-working graphic designers of the time measured their effort on the final result in the intended medium,

but of course they were also compromising on the amount of information they could throw in, and there exist (formal and informal) studies and work towards information augmentation, regardless of the medium. Or, because the original medium is largely unavailable and you want past work to look well on current media (so you try to augment information to make old works look better on LCDs and similar).