From what I can gather skimming instead of using users / groups to isolate processes they are using containers.

It feels like Linux and windows are converging into a single OS

Single-user workstations are usually pets, and it's much easier to manage a pet when every single unit of execution is separated from other units of execution.

It's also much easier to manage each application with it's own root for everything, rather than multiple applications installed into a single root.