Why do nesting birds lay fewer eggs than brood birds, while both parents look after the offspring

Why do nesting birds lay fewer eggs than brood birds, while both parents look after the offspring, and in brood birds, as a rule, only females?

Nestlings of nesting birds are born not fully formed and until they learn to fly, they completely depend on their parents. For the same reason, fewer of them are born than brood birds and both parents feed them, one female simply will not feed and protect the chicks. In brood birds, chicks are born completely ready to get food almost immediately and follow their mother. Therefore, the male does not participate in raising brood birds.