I agree with you here, a simple health tracker is awesome. But also it seems to me that Google has a massive incentive to get as much data about you as possible. Which means releasing devices that collect as much biometric (and location) based data as possible, and setting defaults (just like Maps location history being turned on by default) that will automatically send all of this to Google servers. And as usual with Google, the vast majority will probably be sending their health data to Google unwittingly.