Constructor can only be chained in initializer list, Why

Question

Why C# constructor can only be chained (one constructor calling another) in the initializer list? ex

constructor1()
{
    // do something
}

constructor2() : this()
{
    //do something else
}

Is there a reason that this is not allowed?

constructor1()
{
    // do something
}


constructor2()
{
    constructor1();
    // do something else.
}