Because they are literally a client of the lawyers. We can argue about corporate personhood, but the definition of “attorney client privilege” is very clear. It’s not “attorney human privilege.”
Maybe the world would be a better place if companies (and government departments) couldn't protect communications with legal counsel?
I haven't put in enough thought to have a coherent position, but the argument for the current arrangements seem to boil down to "because that is how it always was". Maybe corporate personhood brought along the rights of human personhood and maybe that is a good thing, but it seems to have just happened by default. Maybe we should debate if attorney client privilege is a privilege of clients, or of humans?
That policy goal applies equally well for both individuals and corporations.
It is not some handout to corporations.
Why are individuals stripped of their rights when they congregate together towards a common purpose?
It's a legal and financial instrument to control other people's money with minimal accountability or oversight.
Take this situation, nobody is going to poll Google employees and ask if they would prefer if Google waived attorney client privilege in this manner and act accordingly.
It's not just a group of folks making decisions, it's a structure for a small group of folks to manage the asset and labor of others with minimal oversight.
Instead, there are other underlying reasons for why laws exist, and it is not because of some silly argument such as "Well, this is what the the definition of a word is, therefore we are stuck and can't do anything about it!".
And other people are questioning what these other underlying reasons are.