The other side of this whole deal is that as a hobby/industry we tend to over produce/import and these have to be sold somewhere, somehow.....
Someone was willing to sell these snakes to PetCo at a great price so they can turn around and offer them at a great price. Retail sales are a science and it is amazing what people will buy just out of human nature. (if you are really bored one day, read 'Why we buy' by Paco Hill,(i think))

Also, How did you get into the hobby? I would bet if you polled reptile hobbiest you would see a high number of folks that bought a reptile at a pet store due to some promo.
I got into the hobby by working at a pet store and one of my fellow employees pawn a really bad bull snake off on me at a great price. The rest is history.