US naval strategy is based on Taiwan. With Taiwan in the fold, China's trade can be effectively blockaded should the situation deteriorate to war. It's a last ditch measure, for sure, but a valuable card to hold nonetheless. China is building more pipeline and rail to de-risk this, but ultimately they want full access to the Pacific. Taiwan and South China Sea militarization give them this.
Taiwan going to China turns the tides of Western influence in Asia. Many nations friendly to the West would "switch sides", including close Western allies like Japan and South Korea. This would have tremendous impact to the West's economy, jobs, cost of goods, cost of energy, etc.
Taiwan is perhaps one of the most important subjects that will define this century. There's a reason all eyes are on it.