US & Russian participation on the International Space Station.

[Anomalocaris]

So the US would need to show it can continue to deliver more on each of the areas where China is striving to catch up and out do the US.    Ditching a nominally international space station would clearly not serve the greater national goal of power.

The Universe and even the Solar System are so vast that no nation will be able to explore everything, even if that is all that they did.  If China wants to be "first", so what!??

China doesn’t just want to be first.   China wants, as the US and USSR wanted during the Cold War,to be perceived as a more promising long term partner in space endeavors because the she is seen as the ascending power with not only adequate capability and reliability now, but greater long term growth potential in the future.  Ie, you can reliably accomplish more in space in the long run if you build a partnership with China rather than the US.  

Ditching ISS would be an immediate shot in the own partnership reliability foot for the US, and also be perceived as a shot in the manned capability foot since the US would have no other manned mission until Artemis lands a man on the moon, which at current funding levels might not happen for a number of years.    In any case, people who look at space travels as more than a feather in cap would perceive manned space station as the bread and butter and raisin d’etre of manned space travel, lunar landing is just a stunt.