Appease the huge audience of Android
Looking at the overall market share of Android (around 71%), offering smooth payments to Android users is never a bad idea. With an estimate of about 3.6 billion users worldwide, Android is the main mobile platform in the world.
Google capitalizes on this huge audience by creating a simple sign-up flow to use Google Pay. If the user has a Google account (which almost everyone has), the Express Checkout button uses the personal data stored for a swift purchase journey. Key data such as name, address, and payment methods are safely stored and inserted, and 3DS verifications are simplified due to the biometric verification in the authentication process.