Why GNU coreutils/dd is creating a dummy file more efficiently than D's For loop?

[BoQsc]

This code of D creates a dummy 47,6 MB text file filled with Nul 
characters in about 9 seconds

import std.stdio, std.process;

void main() {

	writeln("Creating a dummy file");
	File file = File("test.txt", "w");

    for (int i = 0; i < 50000000; i++)
	{
		file.write("\x00");
	}
    file.close();

}


While GNU coreutils dd can create 500mb dummy Nul file in a 
second.
https://github.com/coreutils/coreutils/blob/master/src/dd.c

What are the explanations for this?