Science fiction has been rather curiously given to monarchical government. 'Curiously' in the sense that (at any rate to 'Murricans) it is a form of government associated with the past, and certainly not with rocket ships, monorails, food pills, cyborgs, or the rest of the retro-future paraphernalia that sci-fi still loosely connotes in the popular culture. And even, with a reservation or two, in SF fandom.
The situation in fantasy is somewhat different. In spite of urban fantasy and all the rest, fantasy still connotes first and foremost a setting rooted in a medievalesque past, where kings - and the occasional queen regnant - are perfectly at home.
I have read a number of arguments over the years suggesting that the widespread practice of monarchy in SF says something about the authors who use the trope, and probably not to their credit. (Sorry, no links, but if you want examples, Google is your friend.) Similar critical remarks have been made not just about fantasy authors, but its readers, and the very existence of the (sub)genre.
For my purpose, the virtues or defects of monarchism as a political position are fairly beside the point. Kingship has certainly been widespread, suggesting that it was a workable default position, at any rate in the agrarian age. For an intellectual defense you probably still can't do better than Hobbes' Leviathan. Not to mention that as a critique of anarchism and its cousins, it is hard to improve on solitary, poor, nasty, brutish, and short.
But I would argue - in fact, I will argue - that the roots of monarchism in SF have less to do with political philosophy than with basic story considerations.
Bourgeois representative democracy, classical Athenian-style democracy, classical Roman-style republicanism, medieval oligarchical republicanism a la Venice, military juntas, fascistic fuehrerprinzip, Leninist dictatorship of the proletariat, nominally Communist party-committee oligarchy, pure bureaucratic functionary-ism, and both Iranian and al-Queda style theocracy, all have at least one thing in common: The likelihood of a teenage girl becoming head of state under any of these systems is pretty much nil.
Yes, that particular consideration has rather narrow applicability. But it is part of a broader point: Leadership in all of those systems is in some broad sense a workday job. To be sure, rulership is, in contemporary biz-speak, a 24/7 position. But it is walled off, at least in principle, from all the other dimensions of a ruler's life.
Yes, that principle may be honored in the breach: Presidents and dictators do indeed have personal lives that can and do spill over into their official roles. The spillover can even, at times, be substantial, and have some real consequences. But these are the exceptions, not the rule.
Hereditary monarchy is a different beast. Quoting myself from an earlier post here (and, originally, a now-defunct website), hereditary monarchy is a political system that takes sex out of the bedroom and puts it in the history books.
Admittedly there was not much sex in midcentury SF or F. But the authors of these works knew their history, at any rate Western history. Which, from the Julio-Claudians to the Tudors and beyond, offers ample enough demonstration of the uniquely colorful potential of hereditary monarchy.
Someone in the back row is pointing out that the Principate under the Julio-Claudians was not really a hereditary monarchy. (Nor did the Empire ever quite become one, even under the Paleologi more than a thousand years later.) But that was sort of the problem, wasn't it? With no other constitutional mechanism at hand, a kinda sorta hereditary succession was the least worst alternative, with an added element of uncertainty that ramped up family dysfunction even above the usual royal standard.
And on the flip side, monarchy brings grandeur to family dysfunction. Consider The Lion in Winter. The actual story line has all the makings of a squirm-inducing soap opera. But because it is the royal Angevins (and, yes, brilliantly written) it transcends its soap opera plot.
Or, to put it another way, hereditary monarchy is singularly well-suited to Romance. By fully entangling the personal and the political it provides great story fuel. And story trumps futurism, or even political philosophy, every time.
The Flickr page for the royal headgear above describes it as 'Not THE crown, just a crown.' But the lighting is appropriately cool.