Can you provide more detail? I can't find the paper you are referring to.
It's about building a clustered NFS server on "virtual synchrony", which is another replicated state machine scheme like paxos and raft. The paper really focuses on some of the issues in making the system very fine grained versus previous virtual synchrony implementations, in addition to the issues in general to making a clustered, highly available, multi master NFS server.
That might be part of the reason.
On the other hand, a related paper on the same system by a subset of authors is available: http://dl.acm.org.sci-hub.tw/doi/book/10.5555/866299