Mandated paternity leaves is to provide an equal part contributions towards children for both the mother and the father. Otherwise the mother take most of the hit ( as evidence in countries without it ).
It's also to create gender equality in the work place. If there's only maternity leave then hiring a woman of childbearing age has a higher risk for an employer than hiring a man. This leads to discrimination in the workplace with women having lower salaries, less access to interesting projects etc.. because the thinking goes that she is likely to become pregnant and have maternity leave.
In countries where men have mandatory paternity leaves that are significant this imbalance is greatly reduced.
In countries where men have mandatory paternity leaves that are significant this imbalance is greatly reduced.