So how do you know that?
Why wouldn't russia use a tactical nuke in west Ukraine to destroy tank factories? They already are a international Pariah, that is why they align with North Korea.
The only answer is - to remain the last standing they have. But at some point, they might not care. It is dangerous to put someone with nukes in a desperate position. Putin would not survive retreating from Ukraine - he would be in a desperate position if the odds of war are against him - currently they ain't.
> Putin would not survive retreating from Ukraine
A most interesting question is: Would survive Trump?
Why wouldn't russia use a tactical nuke in west Ukraine to destroy tank factories?
Because the Biden administration communicated to its regime (in late 2022) that this would definitely trigger a massive kinetic response. In particular it indicated that its ground forces in Ukraine would be utterly destroyed (as Putin knows it is very much capable of doing).