Google has a habit of keeping its launchers exclusive for its own hardware line. The Google Now Launcher was exclusive to the Nexus 5 for quite some time, and the Pixel Launcher is still only available on the Play Store to Pixel devices. Yes, installing the APK off sites like APK Mirror was an option, but not all of the features were intact.
However, us enthusiasts have a habit of getting our way with these things.
Modified Pixel Launcher for all devices hits version 2.1, brings new Oreo features and much more was written by the awesome team at Android Police.