TikTok hides upload dates on the FYP because people assume newer videos are better. Older posts can still blow up later when the algorithm picks them up, so creators shouldn't delete anything.
Have you ever noticed that videos on the FYP never show the upload date? TikTok does this because we tend to see something new as better. By removing the upload date, TikTok prevents you from assuming a piece of content is good or bad based on how old it is. This is why you should never delete TikToks. They just might find an audience at a later date.
