When you get sucked into reels, you go from "here" to "there," and in the process, while you are "there," your entire whole self is destroyed. The same psychological phenomena happens to gambling addicts, alcoholics, or users of heroin. It has fewer physiological downsides and side-effects as those things; the only material loss you have is the loss of time.
But far more remarkable than that it's simply a waste of time, and rarely articulated, is this psychological loss. The destruction of the self. That echoes through a person's life, to their relationships, their self-construction, etc. It is those echoes that we are now dealing with on a mass sociological scale.
By the way. "There" has a lot of upsides too. People can be creative, productive, expressive while they are "there" too. Creating, being funny, being social, etc. That's why this is so hard.
So there's a point here that TikTok is competing for leisure time that in its absence has a better chance of being imaginative but I think that undersells the creativity of social media to a degree.
Long-form writing ask us to choose a subject and then focus deeply and deliberately on it. It's more demanding and more rewarding.