Comment by jonenst

Because AFAIK the filesystem is at the same time a huge API and designed for a different use case. I can think of the following examples:

- very flat structures: storing hundred of thousands of files in a single directory will fail

- designed for local disks and NFS is a leaky abstraction:

  - running a system using on locks will fail

  - cache behaviors work fine for the "humans browsing files" usecase but not so much for other cases

probably many more reasons