Company wide code sharing is also why you wouldn't want a monorepo. By having it in a monorepo you require a coordination effort on all changes even if it would be ok for people to be using different versions.
There are ways of doing this in a monorepo (by copying code to a new target for instance) - the difference is that you don't need to pay the price of versioning with every change.
Of course. Thats why this is one of those holy war things. Its trade offs all the way down.