If he said for example a day earlier "I will attack" NATO countries could have moved a few troops to protect their embassies pre-emptively, which would have likely been a very shrewd de-escalation, as attacking NATO troops directly would have risked an unintended escalation.

After he has attacked, he has the initiative, and can threaten ww3 if any NATO troops enter the combat zone, and a few troops are not much use anyway.

Timing.