I imagine the number of people who don't unlock their iPhones in ≥24 hours is a vanishingly small percentage of the userbase. Especially since with new iPhones, just looking at the lockscreen with your face unobscured is enough to unlock it.
Apple’s scale is so large, it’s easy to forget even tiny percentages are still actually really significant in absolute terms.
I can see this being too hard to explain compared to “reboots after 72 hours.”