If you've got a 10M+ LOC project and you're not doing some kind of distributed build you're throwing money and time away.
Large code bases built and linked with open source toolchains have solved this with, for example, thinlto. And by "large" I mean orders of magnitude larger than the mentioned game.
But yeah, outside of some of the largest of FAANG software, there aren't a lot of codebases that can truly justify 100m lines of code. I'm sure GTA VI is over 100m lines but can be cut down to 10m if that was a priority (it never is)
Especially for games or OS development, you might have shifting toolchains and SDks. Different teams may move out of sync because different teams want different things at a given time.