alt Hacker NewsThere's a massive open source app ecosystem for Android which is far larger than the subset available in F-Droid. Open source does not imply private or trustworthy. Completely trusting applications with access to all your data with no insight in to what they're accessing or sending to services means you wouldn't know if your privacy is being violating anyway.
The (desktop) Linux security model is different. You trust the distro maintainers in the same way you trust the GOS devs, and instead of "app sandboxing" you use user accounts, containers or VMs to protect personal information. The Android security model makes sense in the context of laypeople using mostly commercial malware on the stock OS however.