Whoever sold those chicks was unskilled or sloppy. When I was a kid and my dad would order chicks for our ranch, we rarely had more than 5 or 6 baby roosters for the one or two thousand chicks we had ordered. In addition, at least for the commercial sales, the hatchery would pack an extra 4 chicks per box of 100 to cover losses during shipment and to make up for any males we accidentally received.
It was a tiny farm. He ordered maybe 30 hen chicks. He got a bunch of young roosters mixed in . (These numbers are just a guess). This was in the mid 1970s. Don’t know if the ratio is better today because of better techniques.