This is more (or less?) the same as industry best practices, just scaled up. There is a challenge in scaling up, as there is more potential for someone to mess it up. But it's the same technique.
So what am I missing?
That's like saying S3 is the same as ext4, their the same, just scaled up! This is a poor argument, you'll note that S3 and ext4 are entirely different things, not "challenges", fundamentally different implementations.
Google is the only company I've ever worked for that automatically deleted dead code, let alone across a company of 100k+ SWE.
Our internal practice is to delete code if you suspect it's unused, run tests, and if it doesn't affect any tests, go for it. This could be automated, but it is not pressing enough, so we didn't automate it yet.
We could though, and it may even be a good idea, but I still don't get the novelty. But I appreciate your point of view.
The specific topic here is not one of those google problems to me, as I can compare it to other problems we already solved. But yes, we could miss that critical point where a totally different problem domain emerges just from one order of magnitude more, so fair game.
This is one of the details that the blog post goes into. Sounds like it's not as trivial and obvious a problem as you think it is, and you would have benefited from just not dismissing the post because of that.