If a government is competent enough to detect this, they're competent enough to add it to their very own cyberweapon stockpile.

They wouldn't be able to do that for this particular exploit since it requires successfully decrypting data encrypted by the attacker's secret key. A zero day caused by an accidental bug though? There's no reason for them to eliminate the threat by disclosing it. They can patch their own systems and add yet another exploit to their hoard.