I would say a good part of it is FloraFox's excellent point about the hierarchy. The women most in a position to speak out about prostitution and sex work are those in more fortunate positions. Therefore their views and experiences are not representative.
Women who are currently in prostitution may have employers to protect. They may be inaccessible to have their views listened to, because they are working illegally, have been trafficked illegally, are underage, don't speak English, or are hidden for some other reason. They may be addicts who are focused on their addiction and nothing else. They may be in a well known stage post sexual abuse where they are trying to re-write the narrative of their own sexuality and hence lying to themselves about their reasons for being in sex work (massive, massive simplification of the complex reality of that situation, which is extremely common.) The abuse might be prostitution itself or prostitution might be a reaction to previous, even historical abuse.
We know that women in vulnerable situations (care leavers, women in deprived areas, women leaving school with low or no qualifications, addicts, women with mental health problems or learning difficulties on a minor scale, not enough to be institutionalised, enough to make life difficult to navigate, etc etc etc) are more likely to go into prostitution or sex work than women in the general population. We have stats and numbers for some of these categories. Again, these "categories" of people are often less able to speak up, less easily found, their views less easily accepted by many.
That's just off the top of my head.