How are people downloading videos with no watermark?

Hey, i used to run a tiktok account with videos that went viral, like 10-11 million, and I'm noticing people are posting the videos again on different platforms like Instagram. Only I'm noticing that their posts don't have the tiktok watermark. These are the videos that seem to be doing good on Instagram and since I made the videos originally I want to post them again. Only I'm not sure how these people are doing this, it makes me think they are doing something special that the algorithm likes. Thanks!