When you move, you have a few choices of what to do with all the stuff you’ve accumulated. You could sell or donate most of the stuff you’ve accumulated over the years. Or, you could just move it, because you don’t have the time or the energy to figure out what you keep and how to dispose of what you don’t want.
Most enterprises migrate their data to the public cloud in that second way: they just cart it all from the data center to the cloud. Often, there is no single source of truth in the on-premises databases, so all the data is moved to the public cloud keeps all its redundancies.
Although it’s an architectural no-no, the reality is that most systems are built in silos, which is where the redundancies come from. They often create their own version of common enterprise data, such as customer data, order data, and invoice data.