It is typically due to use permissions in the manifest that aren't declared as not required. (i.e. android:required="false"). In my personal experience, permissions involving cameras are normally the culprit
More information straight from the developer page:
If you request a hardware-related permission — CAMERA, for example — Google Play assumes that your application requires the underlying hardware feature and filters the application from devices that do not offer it.
To control filtering, always explicitly declare hardware features in elements, rather than relying on Google Play to "discover" the requirements in elements. Then, if you want to disable filtering for a particular feature, you can add a android:required="false" attribute to the declaration.