Nuclear has only been used once, before it was known to the world and taboo, and there are plenty of strong arguments that the war was already over by the time the bombs dropped.
Chemical and biological weapons are hilariously imprecise and always back fire to some degree and are largely ineffectual (Look up mustard gas in the world wars for examples of how they were useless at actually taking ground or removing opposition)
And starvation like strategic bomb doesn’t really effect the war fighting capacity of a country and typically increases civilian support for the army to spite the ones inflicting them.
Countries use these weapons (aside from the first) because they are the epitome of “this is scary therefore it will work” but that’s an emotional argument not a factual one.
War crimes cause long lasting damage to their victims but don’t achieve military gains. Because if they worked they wouldn’t be war crimes they would just be war. when we created the list of war crimes scholars and generals worked together to make a list of strategies that the scholars wanted removed for humanitarian reasons and generals wanted removed for being ineffectual.
That and the fact that so few people died, murica and their guns…