In that case, can't you then just un-DRY (hydrate?) the code by branching it for each subsystem? Then each team can keep its own pace, and still cherry-pick improvements from each other, which would be difficult to do if they were simply pieces of code copied all around the codebase.
Yes and no. Once a half dozen components take a common dependency, that dependency tends to grow large and complex. Where each component needed a simple string templating class (for example), the aggregate dependency ends up doing too much and is overengineered. It has multiple layers of abstraction to make the various string manipulation classes "look the same" and therefore justify DRY refactoring.
So yes, you can just "rehydrate" the dependency into each component, but you often end up needing a fair bit of work for each component to untangle the mess and create the minimal dependency that each component actually needs. If you just want to copy the dependency directly, then sure, that's typically pretty easy. But that's also typically a pretty terrible outcome as now you have tons of duplicated code and modifying the dependency implies duplicate work, and worse, duplicate pointless work as you must maintain the pieces your component doesn't even use.
