The discussion seems to be mostly about the moral issues, but it seems likely that the titles being a 'magnet for scams and chargebacks' is more likely the cause.
Payment processors have ways of passing some of the chargeback risks onto the stores, and it's not like Steam itself is chargeback central. If you just want free games, pirating them is extremely easy, and trying to abuse chargebacks gets you banned.
People launder money in the way you describe do that via extremely popular titles (so they can sell the whole account later) or rare items in online games like CSGO or Dota. Not "Incest Simulator 2023".