For one, apps in a Linux distro are generally built from source on distro infrastructure, often maintained by a separate person - the distro maintainer - from the original authors of the software. With the source code fully in the open like this, its much harder to slip in user hostile behavior, without anyone noticing and doing something about it.

In comparison on Android or iOS Autors directly upload unauditable binary blobs to an app store that then pushes app updates without almost any user control, often fully automatically. Sandboxing makes more sense in this context as a result.