In essence, journalling is similar to a psychotherapy session.
The clarity of mind you get after a journalling session comes from structuring things in your head, not in your TfT tool.
Yet, as one would expect, people project that feeling onto a tool — which leads to more time invested.
Ultimately after the N-th session, when you try to use the tool to get more of that feeling — you get the opposite, burnout, and then people switch to a new TfT app for the same cycle.