There might be foreign policy implications but the biggest reason is really nurturing their own tech independence and entrepreneurship.
The US is a barrier to a number of key Chinese goals, like reunification with Taiwan. So of course most of what they do will take the US into consideration.
At valuations of about trillion each, I don't know where else they'd go..
China also benefits massively through all of the commodity hardware they make. Sure, they aren't competitive in the chip arms race, but they dominate all the component and power electronics markets. Think about all the power supplies and other commodity components needed to build a gigawatt-scale data centre.
For each "AI tech giant", there are millions of other US companies that will benefit from broader AI availability. US economy (and US tech economy) != Anthropic + OpenAI.
Every other player, especially domestic, would benefit if USA's monopolies get busted. Ditto usurers, trusts, monopsonies, cartels, etc.
Destroy any hope of profitability, prevent further capitalization, ultimately bankrupt them.
Hasten the popping of the AI bubble.
Drag down the stock market.
Put a dent in the GDP (alleged growth).
Cause investors to pull back, further depressing economy.
Devalue the dollar. Kicking off an interest rate doom loop.
Challenge USA's hegemonic role in the emergent multi-polar (post neoliberal) world order. (Gleefully supported by the ruling coalition's anti-globalist America First faction.)
It all makes perfect sense.