There isn't necessarily an important reasoning; I just find that with a necktie, you can tie a slipknot easier, it is smaller than a belt, etc.
A belt could also be used. I would try to experiment with both and see which one makes you more dizzy. Once you get the dizziness effect, it slowly intensifies and you go unconscious within twenty to thirty seconds.
I prefer a Nylon rope for partial suspension hanging over a belt and necktie (speaking from experience), but that is just me, and what works for me may not work well for you.