I can see how it’d be that way if you signed an enlistment contract in exchange for $X0,000 cash bonus, then 6 mo. later became an ENS. But presumably those details are transparent to the IWC DCO Board, and they take it into account (quickly) when making selection decisions.
You are right about the bonus part - there is also final scrub when the release is granted. Navy wants the return on it's investment for A Schools, C Schools, clearance process and the like.
Even if no bonus was given, if the enlisted sailor has never mobilized -a mob might be ordered before the release for the commission is allowed.
An ugly truth I learned right from regional command at the third signature is - if you are enlisted and selected and have not mobbed - mob might be in your future before your are released to pin. Fortunately - I have mobbed in the past and the last tier signed.