Are there health insurance companies tracking your fitness data?

I was wondering if wherever in the world you’re located whether health insurance companies are offering the opportunity for you to link your fitness data (ie, Apple health, Google fit etc) and adjust your insurance premiums to reflect the level of health/fitness evidenced by your fitness data?

If not, what are some of the likely reasons insurance companies are not doing this?

Also, if this kind of thing is available, would you sign up for it? Why/why not?