>Because conventional capabilities don't matter if they're indistinguishable from nuclear capabilities till they impact.
Then wait for impact and assess. That's the entire point of having flexibility of second strike, to give options other than launch on warning. It's why SSNs exists, to make space for conventional warfare. It's the posture major powers have adopted to reduce or mitigate unknowns in case of peer warfare where both sides are going to throw everything at each other. Because they'd rather wait to be sure than end the world on a maybe.
Again from PRC perspective, almost every conventional US capability are already indistinguishable from nuclear. Especially stand off / beyond visual ordnance that will be used against PRC soil in initial SEAD wave or whatever used to penetrate A2D2. At minimum they threaten the entangled PRC conventional/nuclear infra, which is direct attack on PRC nuclear forces. So do we expect US never to attack PRC mainland? We can hope not, but it's mentioned in enough wargames / policy / think tank papers that it can't be ruled out. So a proportional conventional PRC counterstrike can't be either. Even if it elevates chance of strategic retaliation.
The best that can be done is set expectations that retaliation will be proportionally conventional before moving up the escalation ladder, i.e. US Lancers hits Dalian shipyard building new PRC carriers, PRC notifies US via hotline that 10 conventional hypersonics is going to sink CVN being retrofitted at Puget Sound within 15 minutes. It's not risk free, but everything becomes risky when things go hot.
Then wait for impact and assess. That's the entire point of having flexibility of second strike, to give options other than launch on warning. It's why SSNs exists, to make space for conventional warfare. It's the posture major powers have adopted to reduce or mitigate unknowns in case of peer warfare where both sides are going to throw everything at each other. Because they'd rather wait to be sure than end the world on a maybe.
Again from PRC perspective, almost every conventional US capability are already indistinguishable from nuclear. Especially stand off / beyond visual ordnance that will be used against PRC soil in initial SEAD wave or whatever used to penetrate A2D2. At minimum they threaten the entangled PRC conventional/nuclear infra, which is direct attack on PRC nuclear forces. So do we expect US never to attack PRC mainland? We can hope not, but it's mentioned in enough wargames / policy / think tank papers that it can't be ruled out. So a proportional conventional PRC counterstrike can't be either. Even if it elevates chance of strategic retaliation.
The best that can be done is set expectations that retaliation will be proportionally conventional before moving up the escalation ladder, i.e. US Lancers hits Dalian shipyard building new PRC carriers, PRC notifies US via hotline that 10 conventional hypersonics is going to sink CVN being retrofitted at Puget Sound within 15 minutes. It's not risk free, but everything becomes risky when things go hot.