They love tiktok because the algorithm works extremely well.
No other social media actually targets you as well as tiktok does. Instagram is constantly trying to shove you in the direction of whatever makes them the most money even if it’s entirely unrelated to your interests. YouTube is clueless to what you like with shorts. Tiktok surfaces new content that is basically unseen anywhere else (thousands of views not millions) that perfectly fits your interests.
Could other platforms do the same thing? Probably: but they’re too short sighted to do so.