Provided the Buyer-of-6 would use a dozen in a month, IMO the only rational reasons for buying 6 at a time at a higher price are:
- Storage space, either in fridge, on the counter, or in a cooler; or
- Their regular prep (e.g., poaching) requires the freshest possible eggs.
There are innumerable irrational reasons.
Where I live, eggs must come from “free range” hens. Everyone was dreading a huge price increase when the law took effect, but the increase never came. The prices I see for eggs of various producers varies considerably, with house-branded hovering around $3.50/doz for Large A-grade. It’s been a LONG time since I saw a pale, anemic yolk.