Someone much more tech savvy than me should try to use Charles Proxy on an iOS device and see how often your phone is communicating with Apple servers. It’s pretty wild.
I think everyone knows that a good part of the Apple app ecosystem relies on syncing data. I don't think anyone is surprised that a daemon is syncing your photos between your devices/cloud. Add podcasts, ePubs, etc. and you're going to have a busy network on your device. It's a reason in fact I use the cloud, sign in with my Apple ID. I can lose my machine but not my documents.
Maybe the thing that is more along the lines of what you're suggesting though is the network traffic that is seemingly less useful to the user (but useful to Apple). Various frameworks have appeared on the OS that allow apps to share analytics (pretty sure though these are the analytics that you are asked if you want to opt out of on an install/setup).
But because it has become so easy to do (in part because there is a framework to handle it, but also just the ubiquity of the presence of a network) lots of, I think, dumb data is collected to no doubt satisfy management/design as to whether some feature of an app is being used or is not being discovered.
The ubiquity as I say has made it too darn tempting for all parties (Apple and 3rd) to become lazy about how their apps are being used and to become too data hungry themselves.
I had someone recently ask me how I get feedback from my blog posts since there is no comment section, no analytics .... they wondered why I bother blogging at all.