It's not "structurally sexism", it's biology.
Practically no women ever will make it through the entirety of a pregnancy without needing (not choosing) to take some time off work if she works a full-time job. Even if this is just a single day of delivery.
Generally though, it's much more than a single day that needs to be taken off. In contrast, at no point in a woman's pregnancy does the father need to take time off.
There is nothing sexist about this. It is more efficient to extend one person's required time off than it is to give two separate people time off. An extended maternity leave generally means that one company needs to find one replacement or otherwise shuffle work. Maternity + paternity leave means you need to do that, 2x.
I fully support longer paternity leaves because I do think it is important for having equality in the workplace. But the idea that it's society that is sexist in this regard is ridiculous.
Honestly I don't think we will really have equality until babies are grown in test tubes, and that's not society's fault.