Using blockchain as the underlying data structure for Steem offers several significant advantages:

1. Decentralization and redundancy. Rather than being run by a central company, which could fail, be acquired, or face legal issues in its jurisdiction, the Steem blockchain is operated by a network of independent witnesses located all over the world. A large and healthy community of witnesses means that even if bad things were to happen to a number of them, the network would continue without issues.
2. Third-party development. An open, distributed, consistent underlying data structure allows anyone to build upon it, which is why there are already dozens of companies operating as interfaces to the Steem blockchain, as diverse as DTube, Steempress, and Ulogs.org.
3. Persistence. The distributed open ledger of the blockchain means that data committed to Steem will remain in the collective memory of Steem as long as the system continues to run. No secret removal of content by centralized authority, no losses to technical issues, no foreign intelligence services who can conduct disinformation campaigns and then cover their tracks. If something happens on Steem it is traceable and provable.