[jsheard]

In real terms dark modes have gotten darker too, at least on mobile, due to the proliferation of OLEDs with infinite contrast. #000000 went from "the darkest grey the display can manage" to "no light whatsoever".

[zerocrates]

Also shown on the chart, to a smaller degree. And more noticeable on mobile probably where there's lots of OLEDs and concern about battery usage.