They use a pole dildo becouse the models prefer it to human contact. They get paid extra for vaginal and anal penitration. But they do not want the pyhsical contact that handling a dildo would couse.

also it is illegal in the states to show or record intercoures while in bondage. I have even seen them use a strap on dildo when a master was using a sub on waterbondage. Odd Laws in the states some times.