It's much deeper than exposure. It's closer to an "ecosystem" model. You're likely to create playlists in a service. You will find channels that you like. You will find that some artists are not available in other services. You will find that an interface is better. You might find their "you-might-also-like" algorithm is better. I tried Google's music system for about a year before switching back to Spotify (the irony being that Google Play Music didn't play well with Google's Assistant if you have more than one Google account).