It's a very old impulse and not really limited to corporate group-think. "I'm gonna obfuscate my code and encrypt my data so nobody can STEAL my work!!!" said the programmer of previous decades, oftentimes experiencing a fit of egotistical paranoia over a relatively small personal project.
The same kind of mindset that thinks that the world would operate better if everyone used Bitcoin and trusted no-one.
Often it seems to simply be out of complete delusion about the value of what they've done. I interviewed a guy once that brought in a disk with a horribly crappy little mail client for Windows he'd written that was totally uninteresting to us.
I took one glance at the code, and it confirmed what we'd learned during the interview (he was turned down).
Yet he was terribly concerned with getting the disk back to ensure we wouldn't steal his mail client code. The interview was at Yahoo - it's not like we didn't run a vastly more complicated and advanced e-mail system. And not like there weren't dozens of open source mail clients that were far superior to what he brought in if we for some bizarre reasons should have wanted to "steal" code for a desktop mail client.
The same kind of mindset that thinks that the world would operate better if everyone used Bitcoin and trusted no-one.