I don't understand why it would ever be useful. Either you want it on, or not. Imagine if your mute button decided to reset every now and then. Pause button, or flashlight?
Basically nothing else works like that.
In fact figuring out how to turn off wifi with the combination of Airplane mode and wifi button just about blows my mind every time I try. So complicated.
Imagine you're not good at using computers. I've seen people accidentally turn on do not disturb and be unable to figure out why their phone isn't ringing so they think it's broken.
We are in a small minority of 'power users' - iPhones have hundreds of millions (billions?) of users across the entire world.
That's happened to me. I had to google it, turns out there's a physical switch I never used on the side of the phone that enables it and pushed accidentally.
IMHO, these are not good excuses to avoid a clear interface. If the rules are simple and clear, and presented clearly, even the dumbest of the dumb can learn them. Trying to guess and out-think the user only ends up in more confusion.
When you disable wifi/bluetooth via the control center, pop-up text appears saying exactly what that means. I'm not sure how they could make that more clear. It still may not be your (or my) desired default, but I at least understand the reasoning.
Tiny, wordy, brief text after the button press is not what I'd describe as clear. If you need to add "comments" to a (now three-state) button, it's a sign that the interface needs work.
It's extra complexity in the form of rules added to what was previously a simple to understand toggle button. That it goes against historical norms, reduces privacy, and wastes a bit of power is the icing.
My guess is accidentally disabling those services via control center was a common issue.
I’d rather it be the other way, but that’s probably why it’s not.