Did some quick reading on Eileen Gu, seems like its more for exposure and potential future sponsors/income as she is also a model with current overseas sponsors.
China doesn't recognize dual citizenships, and she dodges the question whenever asked about it. Her response is: "I am American when I am in the US, I am Chinese when I am in China."
She also made the announcement to represent China when she was 15 years old, so most likely she had some other influence in her decision making (her mom, "expert in China investment at Fusion Investment in San Francisco").
This was pretty funny though, her post was shared on Weibo and subsequently blocked/censored shortly after:
