I would propose that is because Americans (both Christian and non-Christian) have confused Conservatism with Christianity. (I don't really blame the non-Christians for their confusion. Conservatives conflate the two often enough that even the Christians are confused.)
Lewis, to the best of my knowledge (and I've read most of his works), didn't invest much time in political activism—much as Jesus was content to pay the Roman soldiers his taxes due and return to teaching.
(I'm a bit of a politico, myself, but it's just a hobby. Or my Malcolm Reynolds side coming out. I don't mistake it for my faith. Bush and Obama are both equally bad news in my book.)
Careful of the No True Scotsman fallacy. It’s super common for people in certain groups (e.g. Christianity) to say, “Oh, but real Christianity doesn’t believe or condone X, Y, or Z” while, in fact, huge numbers of people who self-identify as members of that group do, in fact, believe or do X, Y, and Z.
Sure. But it's just as fallacious to assume an author is contradictory because “Christianity” was redefined in another country after he already died.
Words can have different meanings depending on context, that's normal, but just like when we're writing software, we have to establish the context before we'll get anywhere.
Religion isn't really relevant to the quote as far as I can tell. While various religions can have many and various authority structures, not all do, and of those do, many if not most aren't theocratic. Both tyranny and political imposition by busybodies constantly seeking protect us from ourselves exist in purely secular forms. Bringing religion into the discussion just distracts from the point.
Lewis, to the best of my knowledge (and I've read most of his works), didn't invest much time in political activism—much as Jesus was content to pay the Roman soldiers his taxes due and return to teaching.
(I'm a bit of a politico, myself, but it's just a hobby. Or my Malcolm Reynolds side coming out. I don't mistake it for my faith. Bush and Obama are both equally bad news in my book.)