That’s not a cost for Tiktok though, rather the opposite. They just need content to keep going, they don’t need to make individual creators rich necessarily. From their perspective the more control they have over who is popular, the better.
It could become a problem for them if another app offered creators a better deal, but such an app still has network effects to contend with (you can offer creators a better deal but if the viewers don’t follow them it won’t work).