Libmodule, even in its _easy (high level) APIs, is targeting a smart and hopefully large audience.
Consequently, it is up to developers to understand and observe any pointers’ scope.
It means that any data passed to its API is trusted; it’s up to implementer to actually be sure that eg: a registered topic pointer stays alive until it is needed.
This is often accomplished by using global/static variables or heap-allocations.

Libmodule chose to minimize internal heap allocations to avoid performance issues or enforcing a behaviour to developers, that in my opinion is much worse.
Note that instead map and stack APIs are more flexible about it, offering to eg: duplicate hashmap keys.