There absolutely is a sound commercial justification to share research: long-term growth through advancement of the field. (Deep learning would never have made the progress it has without open research!)
If this seems quaint, it’s because we’re too accustomed to short-term, transactional, Wall Street thinking.
Might as well get some dubious medium term gain rather than spend a bunch of money on security for nothing.
For very good reason, because that's exactly how they behave in all other areas. The question remains, why do they appear altruistic when it comes to sharing papers?
I find it hard to believe that it's actual altruism. It's far more likely that it's transactional behavior that just appears altruistic from the outside.
Out of all of the companies in the world, I wouldn't put Google near the bottom of the list in terms of stuff they've discovered and released to the world.
I heard that Dodge v. Ford Motor Co. was an important precedent in the US. https://en.m.wikipedia.org/wiki/Dodge_v._Ford_Motor_Co.
My wikipedia link above in turn links to https://en.m.wikipedia.org/wiki/Shareholder_primacy, which says in the last paragraph: "The doctrine waned in later years."
This probably confirms what you say, but I'd be interested to learn about specific cases.