Todjaeger
Potstirrer
Mainly due to public opinion I guess. It would be uncomfortable if a concerned public stated pushing governments to cut back on aid to the Ukraine due to the nuke angle. People are aware but don't necessarily like to be reminded of what can happen if things reach the stage where nukes are used.
I think most of are here are of the opinion that if Russia deploys a tactical nuke; NATO would intervene in the Ukraine but the question that then arises is how would Russia respond?
Another uncomfortable consideration is what the potential outcome might be if a nuclear-armed state is permitted to seize territory from another by virtue of it's status as a nuclear-armed state. Such an outcome could lead to a shredding of the NPT and a worldwide nuclear arms race between different nations with territorial disputes.