From the 70s through the 90s or 00s everything was file system-based, and it was just assumed that the best way to store data in a distributed system - even a globally-distributed one - was some sort of distributed file system. (e.g. Andrew File System, or research projects like OceanStore.
Nowadays the file system holds applications and configuration, but applications mostly store data in databases and object stores. In distributed systems this is done almost exclusively through system-specific network connections (e.g. port 3306 to MySQL, or HTTP for S3) rather than OS-level mounting of a file system.
(not counting HPC, where distributed file systems are used to preserve the developer look and feel of early non-distributed HPC systems)