Thank you for this post!
I think the reason these kinds of treatments are popular is due to the likes of Gwyneth Paltrow espousing all sorts of therapies that have no basis in health and science (and no basis in reality at times!).
There is no benefit to vaginal steaming other than a possible method of relaxation (if that's your thing). To me, it's one more obsession over women's vaginas and making women feel they are dirty or "less than" if they aren't constantly cleaning themselves.