Your complaint about Android .apk install is... similar to unsigned software installs on Windows in some cases (not a great argument, I know, but the same as the vast majority of users would be used to).
As for SmartTube, their keys were compromised. Inconvenient, but it wasn't about hostility to self-installed applications.
The main difference is that signing a Windows binary doesn't require any third party review of the app content.
For the former there is: https://github.com/privacyguides/verified-apps-android
Key compromise sucks and is hard to protect against. That said the Apple/Google app stores are also full of scams where people lose a lot of real money:
https://www.macrumors.com/2026/07/27/apple-app-store-fake-bi...