So, they found no evidence for the things that Backpage was alleged to have engaged in. And they decided to bring charges anyway?
There was a similar situation up in Seattle where a group of sex workers and clients got busted. Police referred to the operation a human trafficking ring and called the women sex slaves. The was no evidence that the women had any nonconsensual sex - the police justified their allegations that these women were enslaved by pointing out that some of the women were in the US on expired visas and that it is policy to assume that sex workers on expired visas are victims of human trafficking. This eventually led to one of the clients killed himself.
It's pretty astounding how much damage people are willing to cause to keep people from selling sex.