Don't be idiots. The FBI may say that whether or not they can get in:

1. If they can get in, now people - including high-value targets like journalists - will use bad security.

2. If the FBI (or another agency) has an unknown capability, the FBI must say they can't get in or reveal their capabilities to all adversaries, including to even higher-profile targets such as counter-intelligence targets. Saying nothing also risks revealing the capability.

3. Similarly if Apple helped them, Apple might insist that is not revealed. The same applies to any third party with the capability. (Also, less significantly, saying they can't get in puts more pressure on Apple and on creating backdoors, even if HN readers will see it the other way.)

Also, the target might think they are safe, which could be a tactical advantage. It also may exclude recovered data from rules of handling evidence, even if it's unusable in court. And at best they haven't got in yet - there may be an exploit to this OS version someday, and the FBI can try again then.