Direct kinetic war between nuclear powers is pretty much unthinkable - mutual annihilation if either core territory is threatened. Instead, wars happen through proxies or direct attacks on non-nuclear powers, and then you need the ability to project power short of a nuclear response.

Russia can't prevent aid to Ukraine with nuclear blackmail. The US can't defend Taiwan without ships - it can't use nuclear blackmail itself. And if it doesn't defend Taiwan, not only is Western prosperity threatened, but the entire structure of allies that the US built after WW2 crumbles into a chaos of small parties more easily picked apart.