Bird breeders have common sense guidelines about demanding fewer clutches from aging hens. For cocks it dosen't matter as long as it's giving good chicks.

Producing eggs is physically taxing. The hen digs in her mineral reserves to form the shells. Older hens have harder time recovering and all sorts of problems can occur for the hen and chicks if you keep setting her up for several clutches per year.

Because of the Patriarchy.