Is it possible that corporations generally are getting so large that comprehensively securing their entire network is more or less untenable?
Maybe instead, individual business units (or even smaller) should be independently responsible for security.
You forgot Nintendo.
This is news to me, what happened to Nintendo?
From what I remember a company that had a copy of Nintendo's source code for many N64/wii items got hacked and people took a copy of the code. That company was making some sort of portable hand held N64 thing. Apparently Nintendo had copied more into that copy of the repo than they intended and so a bunch of stuff leaked. It was mostly early 2000s stuff.
Lots of source code for old games and console firmware was leaked about a year ago.