What makes fermentation such a powerful effect on the history of evolution? Why did we adapt to that poison and not others? And why do some people seem to fair better poisoned than others?
On the first question: mithridatism works for most venom. The reason you can build immunity to some toxins and not others basically comes down to whether you're biologically capable of metabolizing it.
Your liver can adapt to alcohol exposure by producing more of the enzymes that break it and its secondary metabolites down. Venom is primarily proteins which are made up amino acids. Your immune system can neutralize it and break it down if it's been made familiar with it.
Heavy metals are typically toxic at the base elemental level so no amount of metabolizing is going to render it harmless or keep it from accumulating. Certain acidic or alkaline compounds are caustic enough to destroy anything your body could even attempt to throw at it.