As if Pakistan is waiting for the global etiquette on the usage of nuclear weapons to change so they can nuke India!!
Both countries can’t use nukes because the other has them too. India has a fast growing economy at stake and Pakistan may be an economic disaster but Pakistani elites have huge assets in the west which can be frozen.
Usage of nukes in the Indian subcontinent has easily calculable first order effects.
In Ukraine it’s entirely different. It is ridiculous to suggest that the US will welcome the destruction of the entire human race if Putin even nukes civilian centres in Ukraine. They won’t. But there are second and third order consequences of such actions which are not in favour of Russia and certainly not in favour of Putin and his friends.