MyRedBook had been operating for more than a decade. It's highly unlikely that the FBI just became aware of them in the last year. Something changed the FBI's position.
Exactly, and if you're FBI, trying to bust prostitution and trafficking, what better tool is out there than a Web site that conveniently spells out contact details for those involved in such a trade. Open to anybody so that screenshots with timestamps can be taken and attached to the case when it's ready to be passed on to the prosecution.
Something must've changed, we're not getting the whole story here.