Conservatism is not defined by smaller government. The root of conservatism is fear of human nature or human impulse and the desire to reign it in before it does harm. This is why conservatism can manifest in favor of either smaller or larger government in a given context. This is why conservatism of the Federalists in the 1790s favored larger government and more government power, and those of the late 20the century favored less.
Burke spoke of the danger of tyranny from above and from below when discussing the French revolution and justified the American and Glorious Revolutions on the grounds that they were a preservation of legal tradition and also fighting against governmental tyranny, while at the same time opposition to France's revolution was born of opposition to mob rule, "rule by men instead of rule by law" and the fear of the tyranny that such a system would lead to in government if allowed to exercise power. Burke also predicted France's descent into dictatorship following this tumult.
The embrace of small government by Conservatives, is a reaction to the New Deal and Progressive eras and it is a marriage of convenience with classical liberalism in opposition to a common enemy. However, as I stated in this lengthy
post , conservativism doesn't have a broad natural base and thus is always working to peel off various groups from the other side and the embrace of such economic neo/classical liberalism is an example of this in action.
