You look at the developer documentation for developing PowerShell cmdlets using C#, and go "look! it says you create cmdlets using C#!".
Well, here is another way to create cmdlets: https://msdn.microsoft.com/en-us/library/jj542520(v=vs.85).a...
Yes, you specify cmdlets using XML. You can point to static methods, remote CIM objects.
It may very well use .NET classes underneath. The implementation details are immaterial to how PowerShell works.
PowerShell is certainly built using .NET - and require that commands are built (or at least execute) under .NET.
However, PowerShell works with objects. An object is a collection of properties and methods that work on the object. Every command in PowerShell must be able to understand the objects, hence a common binary object format must be specified. PowerShell choses .NET objects as it's lingua franca - the PowerShell type system, although it extends it.
PowerShell specification says that commands that specifies parameters must do so with types from that type system, and if they support pipelines they must consume objects from the type system and produce objects from the type system. It is a protocol
This is very much like how sh shells specifies that commands must support arguments as an array of strings and can optionally consume byte streams from stdin and produce byte streams to stdout. It's a protocol
Does PowerShell use the same protocol as sh shells? No. Hence, the commands are different.
You do not like that they are different? fine. Don't use it.
Your pipeline illustration should have been:
PowerShell's cmdlet / object pipeline:
(PowerShell runtime | adapter(arbitraty old-school stdin/stdout) | ironpython runtime | any runtime that adheres to type system)
Unix Pipeline:
(Python runtime) | (arbitrary executable) | (PowerShell runtime) | (Ruby runtime)
Yes, PowerShell raises the bar for commands: They must meet some other criteria than string args and stdin/stdout. But just like sh shells and stdin/stdout executables, PowerShell and cmdlets build an ecosystem. It may hurt to realize that the world one knows is just one possible world, and that there may be others out there where some things may be easier and other harder.
To me, it is an opportunity to learn. Nothing quite like being shaken up a little.