They don't have to publish a working exploit as soon as the embargo is broken, though.
An exploit was already published.
anyone who will use the exploit maliciously will immediately and trivially be able to create a working exploit.
Why not? There has already been a working exploit floating around, at least now it comes from an authoritative source.
Perhaps, but if the exploit code is published folks can double-check that they implemented the mitigations properly.
If there's no PoC, how can you really be sure?