Huh? Basically every sentence in your comment is wrong. Apps can link to other apps. There's an entire framework called Universal Links to support this. And Apple is the only platform maker that requires apps to ask for permission before sharing data for tracking.
Apps can link to other apps, but the receiving app can't track where that link came from (unlike HTTPS where you append anything you want, ie ref=otherapp.com). This has led to the large companies that reverse engineer this via web server hops, S2S calls and SDKs.
