Branch - these guys provide deep links into phones and tools to analyze who clicked on the links and if they worked.
mParticle, Appsflyer, Braze formerly Appboy, Appboy all provide internal app marketing teams tools like mobile push or analytics from the app on the phone.
While NewRelic, letsencrypt (free SSL certificates), crashalytics etc are all developer tools to monitor usage and issues with your app.
In summary majority are 3 classes of traffic: CDNs which cache data, Marketing tools such as deep linking analytics etc, and finally developer tools.
Seems like a missed opportunity for Apple and Google to allow users to opt in or out but send data back to one place and then push that out to all these guys so the phone isn’t sending the same data over and over to so many partners and wasting battery.