Hatcheries would not be able to stay in business if they only used SOP stock, because there isn't enough to go around (in large part thanks to hatcheries diluting breed quality!)
When I got started in chickens, I was so naive. I knew horses, in particular Appaloosas, and could spot bad genetics almost instantly. I'm talking about paint genes, gray genes, dilution of Appaloosa genes to get a better looking horse but that is missing some of the key Appaloosa points that make it a unique breed. But chickens? Two eyes, straight beak, two wings, two legs, lays eggs, clucks or crows...yep it's a chicken. And I could pick a Rhode Island Red from a White Leghorn, or a White Leghorn from a White Plymouth Rock. And silly me, I thought that if I bought Barred Rocks from the hatchery they'd all lay as many eggs as the sales catalog said, and they'd be healthy, hearty, happy birds.
What I got was crow headed, poor laying, narrow hipped, skittish birds that almost turned me away from chickens. Then I got some Ameraucanas...I didn't yet know enough to know that green shanks and green eggs were bad. They were just Easter Eggers, but a hatchery wouldn't lie, would they? Then I got some Anconas...beautiful, but so tiny, and of 15 straight run chicks ALL were cockerels. Not enough meat to bother even processing. They did tick duty in our woods for a season or two. Brown Leghorns...good layers, but more skittish than sparrows and were all about free ranging. Eggs? They probably laid a lot but I rarely found any of them.
So I quit with factory chicks (other than red sex link layers for the production flock) and I have had several nice birds over the years. Buff Orpingtons, Light Brahmas, my current EE x EE and EE x RSL crosses...and by not keeping anything that does not ACT like a domestic chicken raised for utility does, I am coming up with better chickens. In a few generations the stock I have now won't even be discernable in the offspring, but if I choose right I won't be disappointed. Right now I have Millefleur colored, cochin type, feather footed green egg layers. I do like the way they look and am considering concentrating on these birds if they lay well.