Why modules is so strongly limited?

[imbaFireFenix via Digitalmars-d]

Hello my friends!
I'm new user of D language and leaarning how it works.
I'm know C++ and trying Rust, GO and some else and now - D is the 
best language for me

But I'm confused... Many coders was great work and interesting 
features, but modules is so strongly limited!!!

https://dlang.org/spec/module.html
Only one module per file.

but Rust and beta VC++ can multiple file to one module! Why 
implemented this limit?
Why modules not written as mix of C# namespace and C++ 
translation unity? It will be greatly!

But for now for huge project need to do:

~~~ ~~~ ~~~

module M1;

class M1
{
}

~~~ ~~~ ~~~

module M2;

import M1;

public alias M1 = M1.M1;

~~~ ~~~ ~~~

import M2;

int main()
{
     M2.M1 Something;
}

~~~ ~~~ ~~~

Thanks.