Why is it easier to find enduring reactionary texts than enduring texts that state the basic position of conservatives in liberal democracies? That's the puzzle.I think Jacob has answered his own question, actually. Fundamentally, conservatives (in the relevant Burke-to-Buckley-to-Sullivan sense) are liberals (in the classical sense) who worry about cultural decay. That is, they agree with liberals that subjective freedom is the end of the political community, but think that market freedom needs a basis in certain cultural institutions in order to be stable and lasting. Those institutions are always being whittled away by the drip-drip-drip of market freedoms, so conservatives self-avowedly find themselves repeatedly "standing athwart history yelling Stop!" The trouble is, as Jacob says, "history keeps right on going." The drip-drip-drip keeps eroding the cultural institutions, and conservatives have to take some new stand.
To be a teachable classic, a work has to touch something enduring, and conservative texts tend to be caught up in the present crisis. Marxism, too, has produced many such momentary texts, but Marxism also has a theoretical framework that is very different from liberalism's, and so even many of these "conjunctural" texts evince an underlying structure that can sustain analysis independent of the historical minutiae.
I'm just not sure conservatism has such an independent theoretical armature.