It's not just because people forget to turn Wi-Fi back on.
Radios are "off-ish" because they remain on for other Apple devices and services, but off for other uses.
What actually happens in iOS 11 when you toggle your quick settings to "off" is that the phone will disconnect from Wi-Fi networks and some devices, but remain on for Apple services.
Location Services is still enabled, Apple devices (like Apple Watch and Pencil) stay connected, and services such as Handoff and Instant Hotspot stay on.
HN audience doesn't represent the typical iphone user. The typical iphone user appreciates privacy but is less concerned about transmitting devices than about the phone bill. I'm sure there are people who always remember switching wifi back on (or have a true unlimited contract) but most (including me) are not part of that. I see why this feature can be viewed as critical but think it'll be an improvement for the vast majority of users.
Ideally, they would've provided a switch in the settings to allow iOS10 behaviour. Maybe they'll bring that with a later version.
I think they just fucked up.