This is core part of their business model. They can provide unlimited backup capacity, because you can only use them to backup stuff from drives that are connec

This is core part of their business model. They can provide unlimited backup capacity, because you can only use them to backup stuff from drives that are connected to your computer. So this effectively limits your storage space. Unfortunately services where you can backup whatever files for fixed price attract "data hoarders" - people who are storing data just for the sake of storing it.