“Large numbers of people will uncritically follow sketchy instructions and get hacked” doesn’t in any way lead to “and therefore they cannot be trusted with devices”.
“People keep dying in auto accidents” doesn’t imply “ban cars” on the first order, it implies “seat belts and airbags”.
People seem to be ok with needing a license to operate a motor vehicle and those are far less dangerous.
Which incidentally is often just a pretense for other motives?
If computers have suddenly become so dangerous for normal people, and they want smartphones nonetheless, add to them a dumb-mode encouraged at the initial setup, and requiring some third party assistance to turn it off once enabled..! (and forbid apps to change their behavior if it's not enabled)
Here's my article about that from 2021. It's for the devices sold in Russia, but this issue is worldwide: https://habr.com/ru/articles/575626/
And here's more detailed research of two particular devices: https://notes.valdikss.org.ru/trojan-digma/
Nothing is stopping the guy at Walmart or Tmobile from selling them dumbphones, or are you implying they are forced to?
Here is the first iPhone ad:
https://www.youtube.com/watch?v=6Bvfs4ai5XU
The ad depicts it as a mere phone instead of a potentially hostile Turing machine. There is equivalent messaging in the android ecosystem but its advertising is not so ubiquitous.
We could also imagine a 24h delay to get Play Store access with a modal to make them understand the risks.