Because they have their own version called Douyin. That is the original TikTok, by their parent company ByteDance.
I know, but they're different products with different algorithms and regulations.
I assume the person's point in mentioning it is that TikTok is not considered "good" for China by the CCP, yet they want the US to allow it to continue operating as-is.
From what I've heard, TikTok as it's presented in America is banned in China, and instead the company offers "Douyin", which is similar but has a different algorithm tuned for presenting the user with wholesome/helpful content. I've never bothered to confirm how true that is though, so take it with a grain of salt.
It's not a different algorithm, but a different content pool to comply with censorship requirements. But the dynamics are very much the same, even if the 擦边女 are slightly less scantily clad.
So it's only a different app with a different name that serves different content?