Once you reach a certain scale in a particular type of company the repo just becomes another type of org unit. Your giant fish swallows a minnow, it looks good on paper, someone does a half arse integration, then that repo becomes the one. The one that your manager says, under no circumstances no-one commits to, because then it's OUR repo (with whatever baggage that brings)... The org depends on the code, but the org actively resists it like a virus. This kills any attempt at the mono repo at any largish non FAANG org.