Like seriously i spend a lot of time to do my settlements and if no one is trying to invade them then the whole [censored] thing is pointless, some dude told me that they only invade if your defenses are low and i was like "WHATS THE [censored] POINT THEN????", like seriously in my like 60 hours of gameplay i have only been invaded 2 times and the second time solved itself immediately after receiving the message...
Im even on survival so it seem difficulty also dosent affect this...
Honestly the whole settlement thing just looks like a thing they throwed in there for modders to finish.