China won't attack Taiwan because they know they'll lose. Taiwan is a natural island fortress, all it would take is for US to come in, quickly obtain total air superiority and that would instantly tip the balance of the conflict in Taiwan's favour. Not to mention the dominance US has in Naval power to secure the straight.
Then US could easily blockade China's ports, remove them from SWIFT, freeze foreign assets, place sanctions and they would quickly heel.
China has no allies and surrounded by countries that hate them. They are weak.
