NFS violates a number of basic Unix filesystem guarantees. It's well documented that it violates POSIX guaranteed filesystem semantics. The abstraction NFS chose is "filesystem operations don't time out", and implements this by just making your process hang as long as the network is dead - possibly forever.

I'm not sure it's a bad thing that the Unix FS API doesn't do networked filesystems. Everbody is using userspace APIs for remote file access, and the big and varied design space of remote file access semantics doesn't get bottlenecked on 30 year old system call APIs.