I don't know how breeders do it, but it seems to me that with straight run, the odds are more likely to skew to male. More people want to buy sexed pullets, so what happens to the males, and the iffy ones? They get sold as straight run. At least it seems likely with hatcheries, they still want to sell as many as they can. I could be completely wrong, but I've seen so many posts on here about people getting a high number of males with straight run chicks. That's my theory.