The important question is why smartphones are designed around not having root access and computers are?

What are the incentives at play?

The answer is obvious, tech companies wouldn’t have given users access to root control on their computers either if they knew what they were doing and thought they could have gotten away with it.

It is just circular logic claiming smartphones have to be this way, circular logic that provides a rhetorical smokescreen for the process of corporations taking our agency away from us over our lives and the tools that sustain us.