I worked on google3 for years, most likely some of the code I wrote is still there. I've also done a lot of open source coding too. I'm quite familiar with the structure of google3 and it's not as different as you claim - Borg is a bunch of C++ libraries and programs that depend on each other, nothing magic about that.
So I completely disagree that open sourcing code is as hard as rewriting it from scratch. I think if you tried to argue that to anyone outside the Google bubble they'd think you were crazy. Writing code is hard work! Uploading it to github and creating some project structures around it is vastly less work.
I can't help wondering if this is engineers looking for new promotion-worthy projects.
To rebuttal your statements, I seem need to reveal a lot of technical details. You did not mention what type of software you were open sourcing when you were in Google. But it seems our overlap in knowledge is rather small.
I'll leave this open.
But I want to emphasize that what I stated are reasonable reasons for open sourcing by writing from scratch.
So I completely disagree that open sourcing code is as hard as rewriting it from scratch. I think if you tried to argue that to anyone outside the Google bubble they'd think you were crazy. Writing code is hard work! Uploading it to github and creating some project structures around it is vastly less work.
I can't help wondering if this is engineers looking for new promotion-worthy projects.