Where on earth do you play? In most realms I've seen, 90% of the regions are aligned to the capital. And the few that aren't are 75% because of historical reasons and the new lord simply not caring.
A quick check of EC:
Sirion, Westmoor, Perdan, and Ibladesh are all rather evenly distributed. Caligus is capital-heavy. Possibly because Isadril is isolated with no regions that could possibly be in its duchy, and Fontan city is a very new acquisition.
A check of AT:
BoM, Carelia, Coria, CE (although CE is a slight bit capital heavy), Darka, Eston, Suville, Tara are all very well distributed. Talerium and MI are capital heavy, but still not bad.
BT:
Fronen, Melhed, Old Grehk, Riombara all look fine. Sint is 66% capital duchy, but I'm ot sure what the geography is, though.
In fact, out of these three islands, Enweil is by far the worst, with Caligus close behind. Probably the only two that would strike me as regions being unreasonably clustered in the capital duchy. But I don't know Enweil history. And given what I know of Caligus history, I could see how that could have happened in an IC manner.
So, I really don't know what realms you're talking about. Observation bias, maybe? ("I play in Enweil. Enweil does this. Therefore all realms do this." ?)
