Well you aren't wrong. I think it mainly depends on two things: 1) How important is the art to the dev. = how much is he willing to spend on it and 2)Does he have to pay the full commission price even if half of the portraits are already there and only clothing and some facial features will change?
We know ~1k$ was spent on sex soundtracks (moaning, blowjob etc.). But we do not know if the developer has set himself a limit on how much he's willing to spent on character portraits. As mentioned, we also don't know if every variation would cost the same as a completely new drawing or less.
Maybe he only wants to spent 500$ on commisions, maybe he already paid more than that.
I can only voice my thoughts and hope for the best