TikTok lets you easily put your own video alongside an existing video, or reuse the audio from an existing video.

This basically gives you the tools to develop video memes. You'll often see a video or audio clip go viral and then see a bunch of different riffs on it that evolve over time, each a twist on the previous iteration, in exactly the same way you see image/text based memes evolve over time, get mixed together, adapted for a current news story, etc etc.

This sort of thing doesn't work quite as well on platforms like YouTube, the barrier to creation is too high.

Another component of the innovation is to mix lowering that barrier with a strong algorithm to surface the best content, since you now have so much of it.