It's a lot more complicated than that. They need to be able to take the island very quickly with a decapitation strike, while also keeping TSMC from being sabotaged or destroyed, then they need to be able to weather a long western economic embargo until they can "break the siege" with demand for what they control along with minor good faith concessions.

It's very risky play, and if it doesn't work it leaves China in a much worse place than before, so ideally you don't make the play unless you're already facing some big downside, sort of as a "hail Mary" move. At this point I'm sure they're assuming Trump is glad handing them while preparing for military action, they might even view invasion of Taiwan as defensive if they think military action could be imminent anyhow.