Ask HN: What Would Make You Stick with a Fitness App?

I've been researching why fitness apps fail at long-term retention. Most people drop off after 2-3 months, even with streaks/badges.

For those who lift/run/train regularly:

* What killed your motivation in past apps? * Would tangible rewards (not just badges) change your behavior? * What's the difference between a "nice to have" feature and something you'd actually pay for?

Trying to understand if the problem is UX, incentives, or something else.

Thanks!