I read in an article in the Kashrus magazine (in a previous year) that the chickens from some mass Kaporos markets don’t really end up getting eaten by aniyim. That is because often they are sent to the families as is, without being plucked, soaked, salted, etc. and not in a usable form.
I am not saying that is the case with all, but this was a letter written by a kollel woman (IIRC) who wanted to bring it to the attention of the oilam.