I don't think people realize how broadly spread this effect is and how much it causes feedback loops.
I've tried simplified studies of new players joining and leaving realms in both small and large realms which I am apart of, on both Dwilight and Atamara and my general perception is that more new nobles join larger realms. Now, Larger realms usually have less social mobility and turnover of positions, and thus in the long term, most of these nobles are less likely to stay and more likely to leave. The smaller realms are the ones with more social mobility and turnover of positions, but they see very little inward bringing of nobles for the realm, and thus the smaller realms stay small while the larger realms stay big.
Right now it is almost impossible for a small realm on Atamara to grow to be a big realm on Atamara because of simple noble count. Not enough nobles join the small realms to allow them to take new lands and grow larger. In addition, for many realms they don't even have enough nobles to hold all the regions they currently do without problems.
This is a cyclic process which causes a lot of our issues if my guess is correct.
Which brings us back to the estate system. Before, you would just expand as much as you could, and your great wealth would attract people to your realm in order to better help use and maintain it. Now, you need to do it the other way around, but it's not as easy to attract people with the *potential* of growth (and then long rebuilding times) and so most realms remain rather stagnant.
