The mechanics of that position are complicated, and imagining it, I think it would be pretty awkward at best. A lot of sex acts and positions opted for in porn are chosen because they're showy, not because they make for the best experience. Most people (well, of those who are even into anal in the first place) are more interested in favoring positions that can work smoothly and pleasantly, especially given anal intercourse being inherently rather tricky and sensitive.