For loop only ones because layers.add, why?

I have some layers, and I want to add, from the project stack, a null before each layer so I type this:

#target aftereffects


var theComp = app.project.activeItem;
var theLayer;
var dummyNull;
var dummyLayer;


{
    for (var i = 1 ; i <= app.project.numItems; i++)    {        if (app.project.item(i).name == "DUMMY") dummyNull = app.project.item(i);    }    for (var k = 0; k < theComp.selectedLayers.length; k++)    {            theLayer = theComp.selectedLayers[k];                        dummyLayer = theComp.layers.add(dummyNull);            dummyLayer.moveBefore(theLayer);            //THIS LOOP ONLY RUNS ONES, WHY?    }
}

why does only do one loop?