You would be correct to question if there is a first-order advantage to having the most powerful supercomputer. But it is a national strategic benchmark, like precision manufacturing, certain kinds of biotechnology, rocketry, etc.

What matters most might be that China is maturing CPU technology that isn't nearly as congenial for US TLAs to hack in to. It might not matter so much for this supercomputer, but if Chinese suppliers put price ahead of things like opaque management processors, it might lead to tipping the balance away from easily exploitable endpoints.