Except using a nuke is a bright line, and using that first one is a lot harder than using the second, or the tenth, or the hundredth.
And using the second one is even easier if they start thinking, “Okay, we nuked them, and yet, we’re still here…”
It’s been widely understood for decades that the first use of nuclear weapons will almost certainly end up in a full-scale nuclear war. Once that first one goes off, we’re going to be left scrambling to do whatever it takes to prevent that second one. Other than immediate surrender, what could we do to prevent a second nuke?
I’m not under any illusions that we’ll have good odds at stopping a full-scale nuclear war at that point. My point is, a full-scale conventional assault is the only thing that gives us any chance of avoiding the full-scale nuclear war, unless we’re willing to just surrender, as slim as that chance might be.
If we’re not willing to do this, we might as well just surrender now, and avoid the stress.