I will give a couple reasons to include babies who died at birth.
I recently corresponded with someone who did extensive research to determine a genetic disorder in his family. Part of this involved looking for children who died young in the family tree. However, the vast majority of the deaths in childhood that were so much more common in the past were probably just from the lacking medicine and sanitation and don't indicate anything hereditary.
In my family tree discovering multiple infant deaths has helped determine the birth order and approximate years of the surviving siblings by considering the pregnancy time for the deceased infant.
Finally, they are part of the family and the family story. Since they often were not discussed this is really the last chance to give them recognition.
All the best,