Because maternity leave, while a good thing, isn’t one the same level as protecting life.
A business not having flexible maternity leave is not on the same level as actively killing a life. If a company CAN implement maternity leave, then I think the absolutely moral thing is to allow it, and the longer they can afford it, the better.
However, let’s say there is a small Mom-n-Pop store. They have 5 employees. One of their employees just has a baby. However, this small store can only afford limited maternity leave. If they could offer more, they definitely would. It is not immoral for that store to not provide what is ideal if it is outside of their capability. This is now a prudential judgement call. This doesn’t mean they are now actively trying to hurt the mother and child.
So there is a difference.
If, however, a law is implemented to enforce that small store to offer maternity leave outside of their ability, then it is now hurting this small store and could lead to laying off employees, which leaves them even worse off. Not because they want to lay them off, but because they have absolutely no option if they want to ensure their store can remain standing.
There has to be an understanding of economics and the morality behind certain decisions, even if they aren’t the ideal.