Google Play Services is essential for most features a user would expect in a modern mobile phone. For running bank apps (SafetyNet), many maps apps or apps that include maps (eg Uber, Tinder - due to Google Maps API), push notifications, etc. It's absolutely used to lock-in users to the Google ecosystem and discourage them from degoogling.
Those are services that can be provided by others on any Android device, including those sold by Google. The fact that others aren't providing those services doesn't mean Android itself is meant to lock in users (or to collect data / serve ads), only that others haven't found a reason to provide those services. Google also provides many of those services on other OSes it does not develop (e.g., Chrome push notifications and Widevine).
