Why don't world or actor components show up in drop-downs? (UPROPERTY)

Hello everyone.
I’m wondering why when I declare a UPROPERTY in my C++ class and then want to assign an object to that UPROPERTY, I just get the engine classes in my drop-down, instead of all the objects from the specified type. I’m instead forced to use the construction script to assign those objects. Is there a way to get this solved?