You probably ordered pullets and if so most of the hatcheries that I have dealt with in the past are really good at sexing them. I bought 25 Buff Orpington, 25 Black Sex Links and 25 Barred Rock 4 years ago and the only one that had roosters were the Barred Rocks, 2 of them were cockerels. Another year I bought 20 RIR, 15 Silver Laced Wyandottes and 10 White Rocks. I told them to send me 1 each cockerel of the SLW and RIR and that is all the cockerels I ended up with. If you would have told them that you wanted a roo, they would have made sure that there was one in there. lol
I would have ordered straight run had I gotten my coop (I remodeled my kid's old play fort) finished in time and put in a hatchery order. I wound up buying them last minute at a grain store, the very last 15 they had! But the store had ordered straight run (I'm pretty sure) just my "luck" I got all pullets. Betting there are other people who got theirs from the same batch who wanted pullets only and have 5 roosters! I actually placed an ad on craigslist hoping someone who doesn't want the roo they have will give/sell him to me... Otherwise I guess some of my skinny girls that would have been culled get to stay around and give me eggs a bit longer while I order a bunch of cockerels to grow out to select from for breeding next year.