Personally I believe the survivors in the base is a part of the base management aspect of it so I'm not sure what you'd want them to do. I don't think they intend for the base to be "automatic" either, on purpose.Sure, but if you put down your controller and do not actively do anything, the other survivors largely won't either. And that's the point I think, where everything revolves around you doing things. Nothing gets done without you actively doing it. You can't form a group of survivors to take on a mission without you. You have to lead that group of survivors on the mission. Again, correct me if I'm wrong.
They do defend and attack nearby enemies that pose a threat which is what matters the most.
I do think you're correct on the "send out survivors" part since I've not seen anyone do it.