Now a more relevant example:
I discovered a security vulnerability in FB.
1. Publish the vulnerability publicly (legal)
2. Sell the vulnerability to exploiters (illegal)
3. Accept FB's bug bounty reward (legal)
4. Attempt to negotiate a different amount with FB, falling back to #1 (illegal, blackmail)
5. Attempt to negotiate a different amount with FB, falling back to #2 (illegal, extortion)
6. Attempt to negotiate a different amount with FB, falling back to #3 (legal)
I assert that treating #4 as a crime is to use the police powers of the state to protect FB's wallet.
But I also think a lot of these companies are happy to frame negotiations as extortionate if someone has the audacity to counter their offer, and that's bullshit. But it would also be bullshit to try to drive up the price on a real bounty after the fact by threating to let the bountied person run free with a map to your house, so it's complicated and I can see the precedent in thought there.
The act being threatened – reporting your crime to the police – is totally legal, even socially encouraged. It is only the demanding of money (or other benefits) not to do it part which is the crime of blackmail.
If I just went ahead and reported your crime to the police – no crime of blackmail.
If I just didn't – no blackmail (but could be some other crime, such as misprision)
It's only when I tell you that whether I'm going to do it depends on whether you do something for me that blackmail has been committed.