Commercials lay around as many in a year as native breeds do in 18 months, depending on breed, so they get clapped out very quickly and it's not worth feeding them through the moult. The shells become thinner the larger the egg and they're eventually too fragile to withstand the washing, packing and transporting process. They may, depending on early life, have nasty habits with regard to feather pecking, have been vaccinated and be carrying diseases such as mycoplasma, so beware of mixing them with other, unvaccinated, birds.