Could the chinese construct a sufficient anti-missle defence?
China obviously has a lot more resources than Taiwan, but then you have a concentration effect where an attacker can focus their resources on a single target, but a much more resourced defender can't necessarily afford to defend that target. We saw that play out with the UK's nuclear deterrent strategy in the cold war, where they focused on overwhelming Moscow's defenses, and were (probably) able to do it despite the USSR being so much bigger.