I think we are used to using multiple apps for different services because that is how it started. However if we were used to using one app for everything, things would have been different
I dunno, I'm pretty tied into the Apple ecosystem. I'm only okay with it because they're very principled on privacy, and will probably be around for a long time. But all my photos, contacts, and lots of my data are all with apple. I suspect many users have even more tied up with Google on Android.
Many people, including me, use *.google.com as a one-stop shop for all their software needs.