Why does this matter? Centralised systems hold all information in one place, which increases risk. For one, it makes them prime targets for malicious attacks. Even in more innocuous situations, centralisation is still risky because if the system shuts down, everyone loses access; if the system is corrupted, all its data may even be irretrievably lost. In contrast, since the same blockchain data is hosted on multiple nodes, even if one node is shut down, the rest are still available.