The wheel of history turns
I don't think "pining for a bygone era" is quite the right way to put it, Ace. I think it's more like the recognition that it's not entirely bygone - that the wheel of history turns, and everything old comes back again. The alien nature of the setting, in either a historical drama or the sci-fi you mentioned, also highlights the things we recognize.
The conservative wisdom is that things endure, both good and bad; we hope to nourish enduring good, the wisdom of the past, while standing guard against the old errors, and horrors. To go back to what I said about "Downton Abbey," and perhaps add one more line to my post: we've got the aristocracy again, right here in America today, but they lack the sense of obligation and responsibility. The stone-cold liberal manipulation of dependents for political gain, shoveling people into massive bureaucracies to burn as fuel for government expansion, would horrify the Earl from Downton. And the Obama-era "Incompetence Defense," in which political hacks chant "I take responsibility" but never take responsibility for anything, would make him retch.
Plus, if you give the show a chance, you'll get to hear Communism smacked around a bit. Which is always fun.