Here is a quick CSV export of all the concerned hosts (subdomain + domain) I could pick from my database.
https://stan.sh/images/ios_domains.csv
I really want the story behind pancake.g.aaplimg.com
mesu, su: software update
pancake: looks like home sharing? https://stackoverflow.com/questions/26900625/what-is-pancake...
phobos, mzstatic: App/iTunes store, possibly also Apple Music
apptrailers: App Store app demo videos?
streamingaudio: Apple Music?
iphonesubmissions, radarsubmissions: crash report upload
guzzoni: Siri
appldwnld: firmware downloads
gs: firmware signature generator/verifier
albert: device activation
ckdatabase, ckdevice: CloudKit, like iCloud 2.0
keyvalueservice: old iCloud sync service, still used with text shortcuts sync
fmf: Find My Friends
fmip: Find My iPhone
All in all just looks normal, there's a lot of features in iOS/macOS/iTunes etc etc and they all have their own respective hostnames, possibly many for old school random-hostname-based load balancing, etc. Seems pretty normal that your users would be downloading apps (or the phone downloading updates automatically), playing Apple Music, updating iOS, etc. Spammy, but not that big a deal. I'd imagine rather similar from Android by filtering to Google, Samsung, etc hosts.
If you think there is an issue, instead of breathlessly declaring you’ve discovered a disturbing pattern in a system you couldn’t possibly have an informed perspective on, the correct way to handle it is to file a radar at https://bugreport.apple.com/ then come back here tell us your radar number so we can dupe it and add any of our own data that might help with the (perceived, in this case, I would say) issue.