They breed for quantity, not quality.
I think it also has something to do with single combs being recessive and rose combs being dominant? Or maybe it's the other way around... don't quote me on that LOL
No, they are supposed to have rose combs... but I think that it has happened with hatchery birds.
@cluckmecoop7 has a single combed GLW too I think. I might have one actually!