It's a developer decision. But I'd say it's easier to not use dependencies on native because there are more capable system API. I don't use any in my iOS apps, and only one dependency in 20 macOS apps.

Yeah, with iOS for example, you typically need very little third party dependencies for functionality. The main ones are things like analytics, crash reports, etc

I’m not aware of any attacks on native package managers in the past 5 years. The closest would be a poisoned Xcode build in China that wasn’t downloaded from Apple a while back.

Also getting an attack on one of the platforms means at least ~half your users are safe on the other one.