There is a reason to call out Sandberg. The reason is to point out that this "mainstream" practise is unjust. And that the market should not set the criteria on decency.
You could say that "call[ing] out" Sandberg is unjust to her because, as you say, big banks do it too. However, (a) the injustice, in concrete material terms, is negligible in comparison to the lives of those working without pay, and (b) this logic, it seems to me, would suggest that all prosecution of individuals is fundamentally unjust unless one is able to round up each and every similar violators.
You could say that "call[ing] out" Sandberg is unjust to her because, as you say, big banks do it too. However, (a) the injustice, in concrete material terms, is negligible in comparison to the lives of those working without pay, and (b) this logic, it seems to me, would suggest that all prosecution of individuals is fundamentally unjust unless one is able to round up each and every similar violators.