I think it comes down to emitted light vs reflected light. If you're looking into an LCD panel and the light it's emitting is not adjusted to match the environ

I think it comes down to emitted light vs reflected light. If you're looking into an LCD panel and the light it's emitting is not adjusted to match the environment you're in, too bright or too dull, then you will strain your eyes. With an e-ink screen, anything printed, or even a cinema screen, it doesn't usually emit light and therefore relies on the light emitted from other things around you to reflect off of the surface, illuminating the surface of the thing you're looking at. This is more natural and provides less strain on your eyes. On a personal preference side of things, I can't look at bright sources in the evening. My wife is a terror for looking at her phone at 100% brightness, it's blinding if she hands it to me to look at. Where as my devices are setup to dim and be as low as possible in the evening, even the profile on the TV.