I can see why there's no direct integration -- isn't it better for a company to ask permission for your data before using it? Like how if you want to sign up for a website through Facebook or Google, they ask first.
That's precisely how HealthKit and Google Fit work, though. You have to allow them access to the app data. The thing with the Fitbit data, though, is that there is no option to even access the data. It doesn't share it at all and doesn't have an option to share it. You either use the Fitbit website or you don't get to see your data. Some apps have hacked work arounds to get the basic data by scraping web data but it's not a true integrated solution. It's crap.
Ah I get what you're saying. So FitBit doesn't allow other sites to access your data stored. What the heck, I feel like that would damage their utility.
Yeah, and that's what everyone is complaining about and what I think is the single biggest thing to kill the Fitbit. They wanted to lock people in to their ecosystem so that people would want to buy only Fitbit products to have them all work together but, instead, people tended to start with a Fitbit and then move on to other products that actually worked together with the other products they already bought or planned to buy.