A habit tracker app doesn't change behaviour by itself - it changes how visible your behaviour is to you, and visibility is what drives the change.
Think of it in plain arithmetic. If you do a habit 5 days out of 7, a tracker shows you that number instantly, instead of leaving you to guess.
That small bit of honest feedback is what nudges the next decision - log a 5-day week and most people want to protect it, so day 6 happens almost on its own.
Why Seeing the Number Matters
Without a record, a missed day and a good day feel roughly the same in memory a week later. With a record, the gap between 5 out of 7 and 7 out of 7 stays visible, and that visibility is the whole mechanism.
None of this requires motivation to spike or willpower to improve. It just requires a system that makes the pattern obvious, which is exactly what tracking is built to do.