A rationale from the core developer [1]:
> I'm sure there are plenty of system APIs providing this information too, and I don't just mean APIs designed to directly provide the information.
> It's not useful to prevent directly getting a list of installed applications without preventing detecting which applications are installed, so this specific feature request has to be rejected. It would have to be part of a larger, much more comprehensive feature preventing apps from finding other apps. That implies outright preventing communication with non-system components which is a much different approach to applications and rules out a lot of things. [...]
> The request should be for preventing apps from discovering which apps are installed, since anything less than that has no privacy / security value. There's no point in disallowing access to a list while not preventing discovering which apps are installed anyway.
The open issue to restrict app visibility is [2].
[1] https://github.com/GrapheneOS/os-issue-tracker/
issues/149#issuecomment-553590002
[2] https://github.com/GrapheneOS/os-issue-tracker/issues/2197