Should Digital Marketing focus more on Fitness Apps?

During the preparation for my first marathon in Philadelphia in two weeks, I looked at various fitness apps which could make my training more interesting and store all my moves. However, nowadays there is not only one app for this, there are 100s of apps available - to mention only the most popular ones like MyRun, Strava or Runtastic.
When researching fitness apps, I found an interesting article on TechCrunch about Fitness Apps. It seems that Angel Investors and Venture Capitalists provided a lot of money to fitness app startup companies. The graph below summarizes the total amount of dollars invested into fitness app startups from 2010 - 2014.

Fitness App Startup investments 2010 - 2014



 Source: http://techcrunch.com/2014/11/10/venture-investors-get-moving-with-fitness-tech/

This trend is in my eyes logical. Fitness and Health had a big boast during the last couple of years and I feel people became more health concious. With the whole technology of smartphones advancing so fast, it seems obvious that many companies try to combine these two trends.

However, when I tried many of these apps I realized that most of them are a) for free and b) don't have any mobile app advertisements. Hence, I wonder if digital marketers have not yet jumped onto these apps or if the apps don't yet want to monetize their innovations.
I believe the next two or three years will show how many of these apps survive and how the apps will actually monetize, however, I believe that already now digital marketers should focus more on fitness apps and positions themselves well in this market.