interaction/dragging example seems hacky

Here's the code in question:

https://pixijs.io/examples/#/interaction/dragging.js

bunny
        .on('pointerdown', onDragStart)
        .on('pointermove', onDragMove);

function onDragStart(event) {
    // store a reference to the data
    // the reason for this is because of multitouch
    // we want to track the movement of this particular touch
    this.data = event.data;
}

// this is the example onDragMove
function onDragMove() {
    if (this.dragging) {
        const newPosition = this.data.getLocalPosition(this.parent);
        this.x = newPosition.x;
        this.y = newPosition.y;
    }
}

// why doesn't this work?
function onDragMoveModified(event) {
    if (this.dragging) {
        const newPosition = event.data.getLocalPosition(this.parent);
        this.x = newPosition.x;
        this.y = newPosition.y;
    }
}

As per the docs for the InteractionEvent, the `event.data` presumably has the data for the current drag event. https://pixijs.download/dev/docs/PIXI.InteractionEvent.html

Can someone explain to me why we have to store the start `event.data` in the current object? I don't understand why using the latest event (as in onDragMoveModified) doesn't work? To clarify, when you try that code, the result is jumpiness on multi touch