Grandmother may have fed only scratch but I assure you, they foraged in a barnyard with lots of insects to be scratched from cow flop and adjacent pristine pasture in which to find other protein, vitamin and mineral sources. If she lived where insects die off in winter and tender greenery wasn't available, production fell off dramatically and probably no eggs produced through winter at all.
If one is keeping chickens in a backyard and they feed scratch only, no matter what grandmother did, they won't get many eggs at all.
Grandmother had 20 or 30 chickens and was satisfied with enough eggs to feed the family.
People want good egg production from their 4 or 5 hens and unless they put the raw ingredients in, eggs won't come out.
A neighbor saw me at the feed store and asked if he could buy some of my birds. He said his were defective. They were under a year old and all stopped laying. I asked him what he was feeding. He said, "scratch". I said, "yeah, but what else?" He said, "Just scratch". I said, "well, you're starving them. They need chicken feed."
He started feeding a complete layer ration and they resumed laying a couple weeks to a month later.