The thing with bondage is that it is very easy to get it horribly wrong and do someone an injury. Tying people up can so easily cut off the circulation, and then there's rope burns/abrasions/grazing etc, and then there's being able to get them free again, either bit by bit safely, or in an emergency very quickly (without hurting them with the knife or scissors) and so on.
It sounds daft when you've never really given it much thought, but it's like anything else - it really needs to be done properly, with safety considerations paramount and precautions in place in case of emergency.