Why `.insert_entry()` is private for `HashSet` and `BTreeSet` Entry APIs?

VacantEntry and Entry of HashMap and BTreeMap each have a method called .insert_entry(). Methods with this name also exist in the nightly-only experimental Entry APIs of HashSet and BTreeSet. However, these are private, so they can't be called by downstream programmers. Is there a reason for this difference in APIs, or is this just an accidental inconsistency?