To limit what malicious software that runs as one's user can do, one must limit what the user can do, and that's exactly what they attempt to do.
I personally præfer that the user be trusted to be wise enough to run software that he does not trust in a contained environment, and he be given the freedom to control his own environment as he pleases.
Windows has the normal desktop that shows your programs and separate desktops for special purposes. There is a desktop where your screensaver runs. So if your screensaver crashes it is not possible for your screen to show up.
Another desktop is where the login screen is on. Normal programs can’t connect to that desktop so they can’t capture your keystrokes as you type your password.
This isn’t about ‘walled gardens’.
This is completely untrue. You can gain root access on Android and have full access to do anything while still keeping applications sandboxed. Limiting user freedoms is simply an extra thing that came with new mobile OSs.
Many “users” on Unix do not correspond to any particular physical human being.