I've spent a lot of time researching and asking that same question, and I feel like I've got a pretty good idea of the answer: Corporate propaganda created in direct response to the civil rights movement which portrayed corporations as the victims of democracy, in order to frame their future attacks on democracy as defensive and justified actions.
SCOTUS deciding faceless and unaccountable corporations were people via Citizens United then helped turbo charge that shit into the dystopia we see before us today.
While Feulner was focused on economic conservativism, the co-creator of Heritage, (Paul Weyrich, architect of the new right who coined the term "Moral Majority"), was obsessed with social conservativism. Weyrich used a similar strategy to create the social movement that convinces poor people vote against their own interests, and hand control to corporations and elite pedophiles with the promise of an eventual return of American society to a utopia that never actually existed:
Even before the civil rights movement, it's important to remember that democracy in America has been under constant attack by Oligarchs since the very beginning.
Those who have always relied on propaganda to distract from their own injustices by placing the blame for the problems they create, on people attempting to disturb what they view as a "natural order" that places them at the top of a heirarchy, resting on the shoulders of everyone else (mudsill theory).
When conservatives argue that the Constitution should be interpreted by its "original meaning," they are referring to an interpretation that favors this "natural heirarchy."