So what's the point of PowerShell if most new CLI tools from Microsoft aren't PS modules and can't take advantage of the .NET object model, even on Windows (see also winget)? Why is DSCv3 under the powershell organisation if it's just a regular Rust CLI?
I can only speculate, but since there is no more LCM, a binary was needed to properly run DSCv3 on your machine.
But that's still damning: If Microsoft themselves are building their PS modules as ConvertTo/From-Json wrappers for native CLIs (or being shipped at all, like winget's PS module), instead of shipping C# cmdlets and a domain model for .NET, then PowerShell is superfluous and we should be dropping it, even on Windows, for a JSON-aware shell or a more common shell with tools like jq.
I can only speculate, but since there is no more LCM, a binary was needed to properly run DSCv3 on your machine.