There are devices without Google services installed. In this case, the Google API is not available. Without using the Google API SDK, your application can still run on these devices.
eg. consider the Kindle Fire, it does not have a Play Store installed, as well as various inexpensive tablets and Chinese phones. Open source custom builds such as Cyanogenmod also do not have Google applications installed (although many users add them manually).
Although Android itself is open source, Google applications require the seller to obtain a license from Google. I know this because custom builds asked Google not to include their applications. In addition, having their own store instead of the Play Store is attractive to some manufacturers, because then they get a share of the income instead of allowing Google to make all the profit. This is why not all devices have them.
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