I'll note of course that even the truths that existed in the fictionalization took a very small part of what was going on during the time and made it fit the series, and also that I'm not an expert (I would however strongly recommend The Decline and Fall of the British Aristocracy by David Cannadine).
From my point of view, there is something to be said for the stability of the estates, as well as the the fact that they generally are architecturally and architecturally important. When an estate went under, what occurred was essentially a fire sale, pieces being sold off piece by piece. There is also very much a labor demand created by these, now 100+ year old estates to keep them up to date, and to now make them tourism attractions (which helps pay for the upkeep). I'm not sure that's really an elegant defense of estates, but just a few things that quickly come to the top of my head as examples.