Because US recognize both mainland China and Taiwan as one 'China', without specifying which. The internet would like to tell you that China and Taiwan are totally different country but US policy doesn't recognize that.
And changing that policy one week into the conflict does not look good on the optics.
US policy does de facto recognizes Taiwan. For instance, it has an embassy there, it just doesn't call it one; and it sells Taiwan weapons over PRC objections.
The only reason the US doesn't recognize Taiwan de jure is a Cold War era compromise with PRC diplomatic policy, and the fact that the current ambiguity works reasonably well for all parties right now. IIRC, some US political factions advocate for formally recognizing Taiwan (for example: https://twitter.com/ambjohnbolton/status/1250501579070980099).
There's nothing easier to do than for China to point to this policy and say America is sending troops to an internal conflict in China.
I'd say the existence of the de facto recognition is more significant than the lack of de jure recognition. There's no real central authority in international relations, so the official statements and pieces of paper are pretty meaningless without the de facto actions of the countries in question back them up.
> There's nothing easier to do than for China to point to this policy and say America is sending troops to an internal conflict in China.
It's easy for the PRC to say whatever it likes, who else cares is a different matter.
So, no, this issue is not resolved, regardless of whoever says it is.
It is an executive communiqué [1]. There is no treaty. "One China" is based on a statement of convenience. It could literally be reversed with a tweet.
What isn't just buttered-up memos are the Taiwan Relations Act [2] and Taiwan Travel Act [3]. Unlike the joint communiqué, these are U.S. law.
Lots of Americans live in Taiwan. Taiwan hosts scores of American-made military assets defending it from Beijing. And high-ranking Americans are almost constantly in Taiwan. If Beijing attacked Taiwan, these would be among the collateral damage.
> say America is sending troops to an internal conflict in China
Everyone says everything when war breaks out. If Beijing blew up a bunch of Taiwanese assets, taking out a handful of Americans in the process, I see no obstacle to strong political support in America to intervene.
[1] https://en.wikipedia.org/wiki/Shanghai_Communiqué
> treating Taiwan as a sub-sovereign foreign state equivalent
Also nothing from [2] or [3] guarantees American military intervention. Essentially, [2] and [3] solidified the status of Taiwan as 'not a full sovereign'.
This was never the goalpost. The original comment contrasted the legal flimsiness of the joint communiqué with the Acts underlying the U.S.-Taiwan relationship.
> solidified the status of Taiwan as 'not a full sovereign'
Not really. The Acts give deference to the executive branch.
Usually, the U.S. can't sell fighter jets to non-sovereign customers. The Acts created exceptions for Taiwan, so the President could continue paying lip service to Beijing while treating Taiwan like a sovereign nation.
I'm not saying these examples were right or just, I'm just saying I think a statement like that from China would have zero impact on the U.S. defending Taiwan.
If you think Vietnam War was bad, try a war in China.
If China were losing badly enough, they'd throw the nuclear card on the table. It presents a difficult scenario overall, as China can always draw a stalemate by using that whenever convenient: stop or I'll use nukes; it's the ultimate homefield advantage. If you're winning away from your home turf, and you're under threat of being nuked, your population will never support pressing forward (it would never be worth it, gain a bit of foreign land temporarily and lose your cities).
Maybe not so much. The PRC threatens automatic military action if Taiwan repudiates that policy, as it sees it as a move for formal independence. So Taiwan has been forced to pay lip service to that policy whether it truly believes in it or not:
https://en.wikipedia.org/w/index.php?title=Political_status_...
https://en.wikipedia.org/w/index.php?title=Taiwan_independen...
The political situation of Taiwan is very weird, as many of the "official" positions are contrary to the actual positions.
That's the 'beauty' of geopolitics: Do anything then switch and do the opposite as long as it suits your interests.
This is a 70s era policy that is increasingly paid just lip service to.