Fifty Shades of Grey: It's Financial BDSM

In all the press generated by the Fifty Shades of Grey trilogy, three statements consistently recur: 1) the books are making a crapload of money; 2) the books are filled with crappy writing; and 3) these crappy books can only be making craploads of money because they’re about sex. The problem, though, is that the “sex sells” formula really doesn’t really explain the trilogy’s extraordinary, almost unbelievable, popularity. As others have observed, there is a surplus of similar erotica, much of it better written (at least if you believe the assessments of online romance fiction fans) and almost all of it cheaper (in fact, most of it completely free and anonymously available online). So what is it about this particular novel? Why Fifty Shades of Grey? And perhaps even more to the point, why now?