My understanding of the term "optimistic concurrency" is that a write operation can fail if the optimism turns out to be misplaced (so to speak). CRDTs on the other hand always merge deterministically and never fail, even if application level consistency constraints are violated.

This is why CRDTs are rarely useful to me, but I can see how they may be useful in domains that can live with the very weak form of consistency guarantees that CRDTs can provide.