It's one thing for the FBI to contact twitter to say "hey there's this account that's posting instructions on how to make and plant pipe bombs so you should remove it" but a completely different thing for the FBI to say "hey there's thing thing that violates one your arbitrary terms of service so you should take it down".
Why is the FBI spending time and resources looking for TOS violations for a private company?
Why is the FBI spending time looking into _anything_ that's not illegal, period?
You can say no to these requests. Possibly, twitter did.