Google, Microsoft, Facebook and Twitter prefer monorepos but this is not indicative of most large orgs.

You'll notice that those listed have had to customize or creat new vcs's to meet their needs.

https://news.ycombinator.com/item?id=17605371 https://news.ycombinator.com/item?id=11789182 https://medium.com/@maoberlehner/monorepos-in-the-wild-33c6e...

This is appeal to accomplishment fallacy. Because large companies have a lot of money, whatever they do must be great. But this is false - they do what they do because they are large companies, not because it is a good idea.

At scale, managing complexity can require either a lot of coordination, or a lot of careful planning. Large companies (especially tech companies) don't do either well, so they pick architectures that remove choices, and iterate on them until they are workable. And they have the money and workforce to do it.