I have to ask, is assplay with large dildos popular among heterosexual couples?! I've see the rise of pegging but that's a stap-on. I mean do people just get bored? Is it a pseudo bisexuality? Is it just a femdom fantasy?
A little bit of everything. I had a girlfriend who wanted to test small ones, and I was curious. It was like her turn on. About the huge ones I can't relate. Some couples are more creative, athletic and curious about sex.
Today you fear less to be judged, insulted and beaten in the street for your sexuality (not everywhere) and some couples speak to each over, try, explore.