They've invested in capabilities that undercut attempts at AI supremacy by US companies. Every time they put those capabilities to use:

- They look more and more like somebody who can prevent whatever world domination plans appear to be brewing in the minds of US billionaires. They can turn this perception into leverage over other countries by threatening to close their model weights.

- They get to use the improved models to boost their economy's efficacy (they probably think they can put it to use better than anybody else, and they might be right).

- For every $100 that the US paid for a given unit of improvement, they just pay $1. The longer the US keeps this going, the less stable it will become because the sacrifices the US has made to pull it off are causing things like measles and explosive diarrhea and will ultimately lead to unrest. Meanwhile the longer China keeps this going the less likely the US is to stand in their way, because the US will have neglected overlong the things that make it a threat to China (the legitimacy of the dollar, soft power programs like USAID, a thriving economy).

Also they have leverage over US because they've recently demonstrated that they can raise the price of oil. That means that they can pop the AI bubble anytime they want. So the longer the US is dumping everything into model improvement, the more opportunities they'll have to use that leverage.