Three letter agencies approach the executive team directly. A decision to participate has to be made at the exec team/board level. If the CEO doesn't know about it, then the company has some serious communication issues.
"Willingly" is the point of contention. The CEOs complied. Whether they felt like they had a choice in the matter is another question entirely.
Twitter isn't on the list. Obviously someone put up a fight.
Or wasn't asked because nearly all of the content is public already. Or is going to cave after some unknown amount of resistance in the future like Apple, Facebook, and Google did. Or dozens of other possibilities.