Let me start off by saying I completely agree with what you are saying as I think in a lot of problem solving (not just programming) there are underlying assumptions that turn into group mentality (just look at real estate in the U.S. as an example as a majority of people assumed that prices would continue to rise indefinitely) so the true underlying problem gets missed.
The one aspect of your discussion that I tend to disagree with is that these apps you were searching for weren't providing what most people are looking for - motivation. I think based on the fact they are searching for the apps in the first place shows they already have motivation or they would not be searching for such help. I'm not exactly sure how an app would motivate a person to exercise besides being an alarm clock letting them know to get up an hour early to exercise. I probably am missing a potential solution here but I am interested in seeing your app.