It’s the human resource’s department’s job to protect the company from liability. If they’re not protecting the company from renegade managers they’re not doing a very good job.
What makes you think the managers are being renegades? They know the company details that you don't know: we have too many women claiming maternity benefits, we have too many people with skill X and not enough Y, etc. Again, HR's job is to handle the needs of senior management, and only until then will HR act against a manager.
Your hypothesis is extraordinarily unlikely. Google has continuously expanded benefits for men and women going on parental leave over these last years. It would make no sense whatsoever for them to also systematically harass pregnant women out of the workforce. If they were concerned about the costs of maternity, they could just have expanded those benefits more slowly. That would have had dramatically more impact, at less cost, than harassing a woman here or a woman there out.
Expanding benefits while simultaneously harassing those who take them gives the benefit of virtue signalling with less of the cost. Most people who receive harassment keep it to themselves as to be public about it is generally a career ender.
I'm not saying we can't concoct a series of words that makes it seem likely, if you suppose that all the evidence that you would otherwise expect is absent because of flimsy reasons. I'm saying that the balance of the evidence suggests that this is not part of any systematic policy, but rather an intermittent failure of a kind that one would expect given a sufficiently long timeline, even in an organization with the best of intentions.
To the extent that there systemic anti-maternity bias within Google, it is certainly below the background rate of society as a whole. That's not a very high bar to clear, so I'll go further to say that Google is actively supportive of parenting and maternity in a way that few other organizations in the United States are. I can say that as someone whose spouse has had two kids there, and as someone whose teammates have had dozens of kids between them during our time working together.
Even with that, failures like these occur, because that's just what people are like, and we have not designed perfect systems to counter this type of behavior. That's not to excuse -- if the story is accurate, figurative heads should roll. And our systems should be improved.
But positing a systematic policy of abuse like this is cynical and doesn't fit with the evidence. Doing so is less like extrapolating a line from a single data point and more like drawing an entire picture from that point.
There is no need for it to be a systematic policy, it can easily be an emergent behavior. Such behaviors are common when there are conflicting objectives. It's human nature. Good luck fighting that.
That is exactly what the person I was replying to suggested. If the managers who harass aren't renegades, then the harassment is systematic, by definition.