Rio is large, has plenty of gold yet can not even attract enough nobles to have a Lord for every region they control. They are ripe for someone else to actually challenge them. People need to stop simplifying human/player behaviour into one absolute. It takes but 5 minutes of looking across the continents to see that such things are simply not true.
Looking across the continents you see a steady trend of small realms coalescing into larger ones over time.
