animals usually have a reason for killing their babies. Rabbits for instance can have many reasons. With a first time rabbit it can be that they are scared by the whole situation. Rabbits will also do it if they are dehydrated or if they need protein due to a deficiency. Other reasons are that they tried to pull a stuck one out and ended up eating part of it while trying to help. If kits are born dead anyways a doe will sometimes eat them. Sometimes the mom's just get overzealous cleaning the babies and clean off ears or legs along with the sac that surrounds the newborn. If something is physically wrong with the kit, even sometimes internal defects, she may kill that baby. If they feel their nest is threatened by a predator they will eat their babies. That last one comes from their wild instincts, in the wild a doe will eat her young if she thinks a predator is going to find them. She does this to regain the protein she needs to produce another healthy litter as quickly as possible without depleting herself. Then she just has the next litter in a place she feels is safer.
I say all of this because it demonstrates that although animals always know why they are killing their babies, we can only guess at which reason it might be. With rabbits you can make sure they are somewhere they feel comfortable, make sure they have plenty of food and water available, feed them a high protein snack a few days before birthing, and that's all you can do. Taking those measures equals out to a high rate of success with birthing but you still get that one litter every once in a while that doesn't work. There is also sometimes that one mother who just can't figure out how to get it right.
So maybe your hen has her reasons or maybe she is just a bad mom, but you will probably never know either way.
I managed to save three of those eggs and they hatched
