The problem is there are easy and well understood ways to prevent that are easier and cheaper, yet manufacturers decide not to use that.

We have several local-only network protocols for exactly this. For residential use, notably Zigbee, z-wave, or Thread, and all of them have much cheaper radios than WiFi. The key benefit here is local only, no direct internet connection.

The only problem is you need a hub and historically not everyone is ready to set one up. However now that Apple, Amazon,and Google are building them into their devices, tens (hundreds?) of millions of people are already set on that