Why isn't field-wise constructor automatic for structs and not classes?

[Shriramana Sharma via Digitalmars-d-learn]

John Colvin wrote:

> Strictly speaking you aren't calling a constructor there, you're
> writing a struct literal.

Why do you say I'm not calling a constructor?

And that still doesn't answer the question of why can't we have an automatic 
field-wise constructor for classes...

-- 
Shriramana Sharma, Penguin #395953