Maybe it's like in Josephine Tey's The Daughter of Time. When the narrative for the past century and a quarter has been "The victims were engaging in a risky line of work, so obviously they were gonna get whacked" instead of admitting that at least three-fifths of them had no discernible involvement with sex work, perhaps Rubenhold perceived a need for clear, repeated, unrelenting emphasis. Like... if everyone else has always said that every woman targeted by this murderer was engaging in sex work, despite a lack of evidence, I could excuse Rubenhold for pointing out say, three, four hundred times that that's just an assumption.