TikTok does exist in China. It is called Douyin. The reason that they have a separate service domestically is most likely not the addictiveness of it. From the introduction section of Wikipedia's article on TikTok:
TikTok and Douyin have almost the same user interface but no access to each other's content. Their servers are each based in the market where the respective app is available.[11] The two products are similar, but their features are not identical. Douyin includes an in-video search feature that can search by people's faces for more videos of them and other features such as buying, booking hotels and making geo-tagged reviews.[12]
Edit: I see what you mean. For all intents and purposes, I stand corrected.