Yes or he’s afraid that if he gives the order to fire a nuke it will be refused and then he is finished. Firing a nuke at Ukrainian forces on Russian soil is no trivial matter. You end up destroying Russian towns and civilian infrastructure.
Ukraine’s forces are now spread out too much within the Kursk region. He needed to fire the nuke at the beginning of the incursion. But of course that would’ve been before he had the chance to evacuate all the civilians from the area.
I think the realities of all this prove that tactical nukes are pretty useless as a defensive weapon. They seem to mainly have their use for a surprise first strike.