1) I'm the sole developer, so it takes a long time to develop (this was about 3-4 months)
2) I really wanted to integrate health data. The step/distance tracking on iPhone and the Health app is perfect for this.
3) The price point lends itself moreso to iPhone users than Android users.
This feedback only matters if you are focused on making money long term on this. Essentially: what is your competitive advantage that you can actually sustain?
Edit: I'm asking a legitimate question, you can stop down voting.
In actual fact, Apple have just shown their hand with this with the Apple Watch daily goals. It's somewhat similar, yet I think both can co-exist easily.
In fact, I use both. Streaks doesn't rely on the Health app, but once the prototype was up and running it was clear the app was superior with HealthKit integration so it became a bigger part of the app.
Apple are investing heavily in the health-related aspects of iOS. Your argument could be applied to any app that integrates with the Health app.
(Side note: I also make public transport apps for iOS, so I'm well aware of how things can go, with all the rumours circling about transit announcements at WWDC)