All blockchains preserve data in different ways, some choose to use SQLite while others use LevelDB. These solutions work fine for pure blockchain solutions but don't provide the robust features of PostgreSQL.
PostgreSQL is one of the oldest open source relational database systems. With Postgres, a user can store information of any type, such as binary files or even music files. This makes PostgreSQL a perfect fit for the Lisk system and provides the necessary database engine to support blockchain applications. In addition to these features, the backup functionality and fault tolerance Postgres offers is unmatched in the open source space.