It's a roleplaying game, yes, but there's also a competitive element. It's natural for realms to strive to expand and conquer new lands, but the fact that most stable realms are able to hold nearly 1 region for every noble means that it's too easy to hold a region. Yes, we want realms to strive for world domination, and it's up to the game to make it hard enough that it's not boring, and easy enough that players are not discouraged. It's a delicate balance.
I feel like you don't understand the problem. It's not bad that realms can have 1 noble hold a region by himself, it's that their aren't enough nobles for all these lands, hence the freezing and rogue invasion.
When realms have more nobles than regions, they aren't telling knights to screw off nor are knights going I need a lordship, I am out. We just don't have as many players so we don't have as many nobles. The increased density should end boosting fun in a variety of ways that can't always be seen by some immediately but some I talk with are understanding. It's not the end all, perfect fix, but helps a lot and more is constantly being developed to aid the game, but it takes time.
