Thing is, for the common scenario of "safe enough for random users to install" we want some barrier of entry. The market where random creations of a ten year old are acceptable isn't the Apple Store, it's something like Roblox environment for user-created content or some other sandbox that is (a) isolated from the rest of the system and (b) makes it clear that it's likely not to meet even the (already low) standards of the generic Store.

For all the major means of distribution the problem isn't not enough apps, the problem is too much garbage - so the direction of improving end-user experience is more filtering of apps and developers, not easier access to distribution.