I think part of the problem in this case OP is the fact that none of the people discussing the situation in these terms actually know the details of what happened, so everyone is merely speculating against the backdrop of a total void of actual facts.
People tend to think hypothetically in these scenarios when pondering questions such as "why might the young person have said it was fine?" and "why did the police conclude that nothing illegal occurred?", and so on, and I think some people who are saying this stuff don't actually think it would be fine, but are merely speculating to try to make sense of the scenario as they have been talking about it for the best part of a week and have now been told that no more actual details are going to be forthcoming any time soon. So people will fill that void with all sorts of crap as they need some kind of closure to reconcile this week of intense speculation with their need to let it go and move on with their lives.
Humans feel far more comfortable when things make sense to us, and I think that often comments like "perhaps they wanted to perform for money" is a way to make things make sense when we know we're not going to find out the truth.
Obviously I do find it surprising how many people condone prostitution generally and don't recognise its abusive nature and the imbalance of power, but I think that the people applying this reasoning here is merely a byproduct of that general view in society that everything is fine with consent.
I guess it might also stem from the cultural shift on emphasising consent in sexual situations, and everyone (including schoolchildren, etc) having been educated on what counts as consent and what doesn't. Obviously, it's great they're learning about consent, but condensing a complex topic into a brief infographic or video to explain to schoolchildren or the general public in two minutes isn't going to be able to cover complex topics like coerced consent and all the ways that might look. And they're not going to go teaching schoolchildren about prostitution to explain how it works (although who knows, nowadays).
So people who have been taught about consent only know the basics, but you have a bit of Dunning-Kruger going on. And so people create this false equivalence that if there is consent, then literally anything must be ok, because they've been taught that consent is the key, and their understanding of consent is still rudimentary.