I can only imagine anyone buying the data does so only if they believe they can make more using the data. I don't think I know of anyone doing this now (not sure if there is regulation preventing this), but its not hard to imagine a eventuality where your health data/work out information can be used by your health insurance provider.
Imagine a scenario, your bmi is higher than normal and is trending higher in the past few months, so that increases your risk for x and hence your insurance premiums go up. Would you care then?
