I get that it's annoying if you choose not to run Google Services. But from a developer perspective if 99.9% of their target market does run Google Services and they make development of the app easier or provide useful features, I can see why they would choose to rely on them.
You can't access the stepcounter directly anymore, only through Google Fit.
Most location features are only available through Google Play's location API.
You can't even get up-to-date openssl or OpenGL support in your app without Play Services.
Not doing so reveals there actual reason: control. Forcing every manufacturer to ship Play Services and thus being able to force various things on their devices is a major financial benefit. It also ensured that Amazon or Nokia were unable to set up a commercially viable Android Fork without Google.