First, do you have a source for the idea that the women were sexually trafficked? All I can find is that the employees were fined and put on probation for prostitution, and the owner was charged with "soliciting another to commit prostitution"
In fact, the article I found said there was no evidence uncovered of the women being sexually trafficked, although that's what they were first investigating. Here's the quote: "Aronberg would tell a judge in Kraft’s case that investigators
had found no evidence of human trafficking."
Washington Post (Aronberg being the state DA for Florida)
Regardless, if Kraft didn't have knowledge of that, it's still one case vs. 4 (or realistically, 30, but we'll go with what the NFL presented to Robinson), creating the difference of a pattern of behavoir vs one incident.