Huh? On the iPhone you've always been able to slide it.
I blame this on all the other implementation which copied the switch design, but didn't bother to implement sliding…
Absence of verb in label makes it clear what it is.
Meanwhile, on Kindle, it shows a black airplane in a white circle labeled "Off" and a white airplane in a black circle labeled "On". This is a recent update from before where the first was an airplane with a slash through it for Off. In both cases, Cell/WiFi is on when labeled Off, network+radios are on when icon was airplane with a slash through it labeled off.
It's likely a strange bug, but I think it's relevant since you can't _always_ slide it.
Airplane mode used to take a a couple seconds to enable so the toggle felt “stickier” to toggle. When you tapped on the toggle, the round button elongated and stayed in the middle for a split second before hitting the right side boundary of the toggle.
Also, the sliding only works correctly if you press and hold and then start sliding. If you swipe, it toggles regardless of which direction you swipe.