Google is made of many thousands of individuals. Some experts will be aware of all those, some won't. In my team, many didn't know about those details as they were handled by other builds teams for specific products or entire domains at once.
But since each product in some different domains had to actively enable those optimizations for themselves, they were occasionally forgotten, and I found a few in the app I worked for (but not directly on).
ICF seems like a good one to keep in the box of flags people don't know about because like everything in life it's a tradeoff and keeping that one problematic artifact under 2GiB is pretty much the only non-debatable use case for it.