How to move layers into group.

I see two main problems with your code.

One is that the enum should be ElementPlacement.INSIDE when moving an artLayer into a layerSet.

The second problem is moving layers changes the index so you can not loop using the index.

Try something like this:

var doc = app.activeDocument;
var txt = prompt("Input layer group name :");
var layerSetRef = doc.layerSets.add();
layerSetRef.name = txt;
while(doc.artLayers.length > Number(doc.layers[doc.layers.length-1].isBackgroundLayer) ) {
    if(!doc.artLayers[0].allLocked || !doc.artLayers[0].positionLocked ){ 
        doc.artLayers[0].move(layerSetRef, ElementPlacement.INSIDE);
    }
}

That should move all the top level artLayers into the layerSet. It will skip locked layers and the background layer. You could change the layer locking test to change those properties if you want to move locked layers. To move the background layer you will need to convert it to a normal artLayer before moving.

This is one way of doing it...

main();
function main(){
var txt = prompt("Input layer group name :",'');
if(txt == null ) return;
selectAllLayers();
createLayerSet();
activeDocument.activeLayer.name = txt;
}
function selectAllLayers() {
    var desc29 = new ActionDescriptor();
        var ref23 = new ActionReference();
        ref23.putEnumerated( charIDToTypeID('Lyr '), charIDToTypeID('Ordn'), charIDToTypeID('Trgt') );
    desc29.putReference( charIDToTypeID('null'), ref23 );
    executeAction( stringIDToTypeID('selectAllLayers'), desc29, DialogModes.NO );
}
function createLayerSet() {
var desc = new ActionDescriptor();
var ref = new ActionReference();
ref.putClass( stringIDToTypeID('layerSection') );
desc.putReference( charIDToTypeID('null'), ref );
var ref2 = new ActionReference();
ref2.putEnumerated( charIDToTypeID('Lyr '), charIDToTypeID('Ordn'), charIDToTypeID('Trgt') );
desc.putReference( charIDToTypeID('From'), ref2 );
executeAction( charIDToTypeID('Mk  '), desc, DialogModes.NO );
};