Because it's a defensive organisation not offensive, good reason...

Because it's a defensive organisation not offensive, good reason russia won't use nukes because the thing they are designed to protect will see their destruction. Double edged sword .
It's an un-winable war , can see the quality of Russian fighters dropping , best are dead and left with the rest which will only see deterioration and collapse on the front . Hence Germany funding announcement they want ukraine to win but not be so strong to be a threat to Russia's existence .