I think the egg-eater needs something not present or not present in sufficient quantity in their normal diet.How do egg-eaters get started, then? (serious question)
I think the reason that it haunts us newbies is because we have seen our chickens tap everything with their beaks while trying to figure out what something is, and more importantly, if it's edible. My always-dying-of-starvation Barred Rock broke the tip of her beak soon after I put ceramic eggs in the nest boxes as they approached 16 weeks old. I can easily imagine a scenario of a young chicken seeing a real egg for the first time, wondering "What's this?", peck PECK, broken egg. And now "What's THIS?" when seeing the white and yolk.
Each bird has a unique GIT, with a highly variable microbiome, and their needs are different because of that, before one factors in age, sex, laying status, etc. Proprietary feeds are based on averages. Birds at the extreme ends of the bell curve suffer more from that than birds nearer the peak.
Natural selection works against egg-eating. So I think it must be driven by nutritional demands over-riding instinct, as and when it occurs.