Because maintaining the One China principle is what is required to do business with China. For most of this century, trade with China was prioritized.
But that's exactly their point. This isn't a question of politics anymore. It's about every nation's desire for prosperity so the recognition of Taiwan hangs in the balance. If Taiwan was the nation that offers the world more, then naturally it would be the one recognised as true China by all. But it isn't and doesn't. Everything else beyond this is moot. The US has indirectly
threatened to recognise Taiwan. It hasn't done that and probably won't. I don't want to explain why but have a think without bias and you may realise.
The US cannot perform moral posturing while they have their cake and eat it too. It wants to have cheap labour from China for its corporations to continue profiting from while it makes x% of its income from China (without compromise), while it prevents Chinese from saving up and developing their own industries, while it tries to stop Chinese companies from finding global success, while it attacks Chinese sovereignty, while it accuses China of crimes it hasn't been proven of, while it recognises Taiwan. It's really asking for the impossible and it probably understands well enough.
Now, under the Trump regime, trade is no longer so important. And with that, the necessity of the One China principle is also fading.
Trade remains important. You're already wrong. It's the main issue for them. I think you mean trade with China is less important because they seem to be willing to take a lot of damage to seek whatever levels of decoupling is realistically possible. Reasons for seeking decoupling you can speculate yourself. Unfortunately the price has proven to be quite a lot more expensive that Trump's team imagined AND their attempts at decoupling have till this date completely failed. US China trade is still not much lower than it was in the 2010s. Their deficit has been reduced very slightly and it's cost their businesses in tax and in lost profits.
You may actually get a formal recognition of Taiwanese independence soon if the Trump regime is aggressive enough. And do not confuse aggression with desperation.
The successful sanctions against Huawei have only emboldened the Trump regime and convinced them they have the upper hand. This is the reality which China must contend with.
Their aggression is sort of desperation when you look at the macro picture. It's not Trump on a personal vendetta, it's the faceless "US deep state" that directs these strategic decisions to begin taking on China now before China becomes impossible to defeat.
Huawei sanctions haven't been successful if you look at Huawei's bottom line. Granted that may change in some months/years but everythings still in the air. Huawei's OS can eventually become successful. It's all there and the technical problems are easy, overcoming the propaganda and the barriers from entering markets is harder. Sanctions are successful in preventing Huawei from accessing certain Taiwanese chips sure. But that's not a measure of success. That's just the sanction itself. Is it/ will it be successful in preventing Huawei from making and selling smartphones in future? That's the measure of success.
Huawei does not need every 5G market on the planet, at worst it loses western european markets but still has the rest. That's already doing pretty well but sure it could have been better if not for US efforts. Huawei, SMIC, SMEE, and many other less visible players may and probably will make Trump's restriction on the latest and greatest lithography equipment a non-issue. We're arguing over the remaining few percentage points. All of this is like China's won and gone 95% of the way and Trump's trying desperately to delay them from overcoming that last stretch. All it needs is time and strategy shifts and there are plenty of solutions that have already been thought of and discussed even in this little forum.
They have the upper hand only in global propaganda, brainwashing, cashing in on all that for moral posturing, and a military advantage which they are concerned about using because China does not seem to be an Iran or North Korea... which are already nations they leave alone when it comes to kinetic war. China is now like a Soviet Union except with better industry and vastly superior economy and more importantly, better management. What do they attack? Economy and politics.